Themes for virtual keyboard

I think that it is great idea to add multiple themes for virtual keyboard, which apperance for now is fixed. If could be connected with changing theme for application UI or as a separare option in settings.

Start by locating the virtual keyboard implementation and the settings that control application UI themes. Define how multiple keyboard themes should relate to the app theme or a separate setting; done means the keyboard appearance can be changed through the chosen theme controls.

Written by the indexing model from the issue text.