Allow right clicking on the layout buttons in the bottom right corner to configure the corresponding area of the user interface

Fixes #1690454 [[Enhancement] Make main window more customizable by right clicking](https://bugs.launchpad.net/calibre/+bug/1690454)

src/calibre/gui2/preferences/look_feel.ui

@@ -19,7 +19,7 @@
      <property name="currentIndex">
       <number>0</number>
      </property>
-     <widget class="QWidget" name="tab">
+     <widget class="QWidget" name="main_interface_tab">
       <attribute name="icon">
        <iconset resource="../../../../resources/images.qrc">
         <normaloff>:/images/lt.png</normaloff>:/images/lt.png</iconset>
@@ -662,7 +662,7 @@ A value of zero means calculate automatically.</string>
        </item>
       </layout>
      </widget>
-     <widget class="QWidget" name="tab_4">
+     <widget class="QWidget" name="book_details_tab">
       <attribute name="icon">
        <iconset resource="../../../../resources/images.qrc">
         <normaloff>:/images/book.png</normaloff>:/images/book.png</iconset>
@@ -795,7 +795,7 @@ A value of zero means calculate automatically.</string>
        </item>
       </layout>
      </widget>
-     <widget class="QWidget" name="tab_2">
+     <widget class="QWidget" name="tag_browser_tab">
       <attribute name="icon">
        <iconset resource="../../../../resources/images.qrc">
         <normaloff>:/images/tags.png</normaloff>:/images/tags.png</iconset>
@@ -948,7 +948,7 @@ see the counts by hovering your mouse over any item.</string>
        </item>
       </layout>
      </widget>
-     <widget class="QWidget" name="tab_3">
+     <widget class="QWidget" name="cover_browser_tab">
       <attribute name="icon">
        <iconset resource="../../../../resources/images.qrc">
         <normaloff>:/images/cover_flow.png</normaloff>:/images/cover_flow.png</iconset>

src/calibre/gui2/preferences/main.py

@@ -13,7 +13,7 @@ from PyQt5.Qt import (
     Qt, QIcon, QFont, QWidget, QScrollArea, QStackedWidget, QVBoxLayout,
     QLabel, QFrame, QToolBar, QSize, pyqtSignal, QDialogButtonBox,
     QHBoxLayout, QDialog, QSizePolicy, QPainter, QTextLayout, QPointF,
-    QStatusTipEvent, QApplication)
+    QStatusTipEvent, QApplication, QTabWidget)
 
 from calibre.constants import __appname__, __version__, islinux
 from calibre.gui2 import (gprefs, min_available_height, available_width,
@@ -259,10 +259,19 @@ class Preferences(QDialog):
         l.addWidget(self.title_bar), l.addWidget(self.stack), l.addWidget(self.bb)
 
         if initial_plugin is not None:
-            category, name = initial_plugin
+            category, name = initial_plugin[:2]
             plugin = get_plugin(category, name)
             if plugin is not None:
                 self.show_plugin(plugin)
+                if len(initial_plugin) > 2:
+                    w = self.findChild(QWidget, initial_plugin[2])
+                    if w is not None:
+                        for c in self.showing_widget.children():
+                            if isinstance(c, QTabWidget):
+                                idx = c.indexOf(w)
+                                if idx > -1:
+                                    c.setCurrentIndex(idx)
+                                    break
         else:
             self.hide_plugin()
 

src/calibre/gui2/widgets.py

@@ -959,6 +959,7 @@ class LayoutButton(QToolButton):
         self.label = text
         self.setIcon(QIcon(icon))
         self.setCheckable(True)
+        self.icname = os.path.basename(icon).rpartition('.')[0]
 
         self.splitter = splitter
         if splitter is not None:
@@ -987,6 +988,18 @@ class LayoutButton(QToolButton):
         else:
             self.set_state_to_hide()
 
+    def mouseReleaseEvent(self, ev):
+        if ev.button() == Qt.RightButton:
+            tab_name = {'book':'book_details', 'grid':'cover_grid', 'cover_flow':'cover_browser', 'tags':'tag_browser'}.get(self.icname)
+            if tab_name:
+                ev.accept()
+                from calibre.gui2.ui import get_gui
+                gui = get_gui()
+                if gui is not None:
+                    gui.iactions['Preferences'].do_config(initial_plugin=('Interface', 'Look & Feel', tab_name+'_tab'), close_after_initial=True)
+                return
+        return QToolButton.mouseReleaseEvent(self, ev)
+
 
 class Splitter(QSplitter):