[Core] Style fixes.
[Core] Configurable Close Tab shortcut for #1278.
[Core] Register shortcuts in core instance Init().

This way we have nice icons.
[Uti] Smarter ShortcutManager::RegisterActionInfo().

Update registered action info if registered info has empty user text.
[Core] Configurable fullscreen shortcut for #1278.
[Core] Configurable Quit action for #1278.
[Core] Configurable Settings action for #1278.