Clean up tag browser context and config menus a bit.

- When right-clicking in tag browser white space, remove any context menu that depends on having an index.
- Remove general subcategorization menu options from the context menu. These are global, not part of context for the current index.
- Add a menu option to the config menu to open Prefs / L&F / Tag browser. This permits easily getting to the global subcat and display options, avoiding adding more menu lines to the config menu.

src/calibre/gui2/tag_browser/ui.py

@@ -879,6 +879,10 @@ class TagBrowserWidget(QFrame):  # {{{
                 action=ac, group=_('Tag browser'))
         ac.triggered.connect(self.filter_book_list)
 
+        l.m.addSeparator()
+        ac = l.m.addAction(QIcon.ic('config.png'), _('Preferences / Look & feel / Tag browser'))
+        ac.triggered.connect(self.show_tag_browser_preferences)
+
         ac = QAction(parent)
         parent.addAction(ac)
         parent.keyboard.register_shortcut('tag browser toggle item',
@@ -897,6 +901,11 @@ class TagBrowserWidget(QFrame):  # {{{
         # self.leak_test_timer.timeout.connect(self.test_for_leak)
         # self.leak_test_timer.start(5000)
 
+    def show_tag_browser_preferences(self):
+        from calibre.gui2.ui import get_gui
+        get_gui().iactions['Preferences'].do_config(initial_plugin=('Interface', 'Look & Feel', 'tag_browser_tab'),
+                                                   close_after_initial=True)
+
     def about_to_show_configure_menu(self):
         ac = self.alter_tb.m.show_counts_action
         p = gprefs['tag_browser_show_counts']

src/calibre/gui2/tag_browser/view.py

@@ -1203,9 +1203,10 @@ class TagsView(QTreeView):  # {{{
                 self.context_menu.addSeparator()
             add_show_hidden_categories()
 
+        if key is not None:
             # partitioning. If partitioning is active, provide a way to turn it on or
             # off for this category.
-        if gprefs['tags_browser_partition_method'] != 'disable' and key is not None:
+            if gprefs['tags_browser_partition_method'] != 'disable':
                 m = self.context_menu
                 p = self.db.prefs.get('tag_browser_dont_collapse', gprefs['tag_browser_dont_collapse'])
                 # Use the prefix for a user category. The
@@ -1224,33 +1225,6 @@ class TagsView(QTreeView):  # {{{
                                     partial(self.context_menu_handler, action='dont_collapse_category',
                                             category=cat, key=k, extra=p))
                 a.setIcon(QIcon.ic('config.png'))
-        # Set the partitioning scheme
-        m = self.context_menu.addMenu(_('Change sub-categorization scheme'))
-        m.setIcon(QIcon.ic('config.png'))
-        da = m.addAction(_('Disable'),
-            partial(self.context_menu_handler, action='categorization', category='disable'))
-        fla = m.addAction(_('By first letter'),
-            partial(self.context_menu_handler, action='categorization', category='first letter'))
-        pa = m.addAction(_('Partition'),
-            partial(self.context_menu_handler, action='categorization', category='partition'))
-        if self.collapse_model == 'disable':
-            da.setCheckable(True)
-            da.setChecked(True)
-        elif self.collapse_model == 'first letter':
-            fla.setCheckable(True)
-            fla.setChecked(True)
-        else:
-            pa.setCheckable(True)
-            pa.setChecked(True)
-
-        if config['sort_tags_by'] != "name":
-            fla.setEnabled(False)
-            m.hovered.connect(self.collapse_menu_hovered)
-            fla.setToolTip(_('First letter is usable only when sorting by name'))
-            # Apparently one cannot set a tooltip to empty, so use a star and
-            # deal with it in the hover method
-            da.setToolTip('*')
-            pa.setToolTip('*')
 
             # Add expand menu items
             self.context_menu.addSeparator()