Discord-like Quick Switcher (#1588)

* Proof of Concept for Quick Switcher

* Fix crash when suggestions are empty

* QuickSwitcher: Use tab name instead of a single channel

* Rebase later

* Add missing include for <functional>

* Move QuickSwitcher related classes into own subfolder

* Refactor switcher list items

Now, items are responsible for taking the right action when selected in
the switcher list. This should allow for more focused code and
responsibilities.

* Add note about memory management

* Add option to open channel in a new tab

* Add support for using the mouse

* Spawn switcher popup in the middle of the window

Works reliably on i3 at least. Might need some additional testing on
other WMs (and especially on Windows!).

* Add some icons for switcher items

Note that the final design of the list is not final but I do plan to
incorporate these in the future.

* Set Qt::Dialog window flag on switcher popup

Prevents tiling window managers like i3 from trying to tile the window.

* Rename "SwitcherItem" to "AbstractSwitcherItem"

* Add comments about what items are inserted

* Use custom model and view

Still missing: Currently selected item is not highlighted yet. You can
move between selected items with tab and arrow keys though.

* Add helper function to convert QVariant to AbstractSwitcherItem *

* Remove useless constant

* Highlight currently selected switcher item

* Use a different method for centering QuickSwitcherPopup window

* QuickSwitcherModel: Add documentation

* Add default parameter to QuickSwitcherModel::rowCount

* QuickSwitcherPopup: Add comments

* Remove outdated TODO

* QuickSwitcherModel: Init vector with default capacity

* Remove outdated comment

* Add comment about 0 ms timeout interval

* NewTabItem: Simplify interface

* Only fetch opened splits once

This is better than the prior approach since opened splits cannot change
anyways while the switcher is open.

* Use SplitContainer to pass information instead of custom type

* Allow searching for tab titles as well

Before this commit, only channel names could be searched.

* Refactor switcher item interface to be more flexible

Also show tab name and channel name in the switcher list.

* Add documentation for AbstractSwitcherItem

* Add documentation for NewTabItem

* Add comments about {begin,end}{Insert,Remove}Rows

* Remove unused method

* Replace magic size with named constant

* Add change log entry

Co-authored-by: fourtf <tf.four@gmail.com>

src/widgets/Window.cpp

@@ -17,6 +17,7 @@
 #include "widgets/dialogs/SettingsDialog.hpp"
 #include "widgets/dialogs/UpdateDialog.hpp"
 #include "widgets/dialogs/WelcomeDialog.hpp"
+#include "widgets/dialogs/switcher/QuickSwitcherPopup.hpp"
 #include "widgets/helper/EffectLabel.hpp"
 #include "widgets/helper/NotebookTab.hpp"
 #include "widgets/helper/TitlebarButton.hpp"
@@ -393,6 +394,12 @@ void Window::addShortcuts()
         getSettings()->hideSimilar.setValue(!getSettings()->hideSimilar);
         getApp()->windows->forceLayoutChannelViews();
     });
+
+    createWindowShortcut(this, "CTRL+K", [this] {
+        auto quickSwitcher =
+            new QuickSwitcherPopup(&getApp()->windows->getMainWindow());
+        quickSwitcher->show();
+    });
 }
 
 void Window::addMenuBar()