Since Grid View doesn't have a header for users to change sorting
options with, use List View's sorting in Grid View too.

Fix some common anti-patterns with these data structures.

- You can dereference the iterator returned by `find` to access the
  underlying value directly, without an extra `operator[]`/`at`.
- Rather than checking for an element before insertion/deletion, you can
  just do the operation and if needed check the return value to
  determine if the insertion/deletion succeeded.

Emit the dataChanged signal when adding or removing tags from a game.
This both updates the contents of the game's Tags column immediately
(instead of having to wait for the context menu to be closed), and
updates the sorting if games are being sorted by the Tags column.

Use NonAutodismissibleMenu for MenuBar's Options, JIT, and
Tools->"Connect Wii Remotes" menus, as well as for the Tags menu in
GameList's context menu.

NonAutodismissibleMenu allows users to check or uncheck multiple
checkable menu items without closing the menu between selections.

DolphinQt: Replace widespread SetQWidgetWindowDecorations calls with an event filter.

Core & UnitTests: Make overriding explicit and remove redundant virtual specifiers on overriding destructors