KateMDI: Introduce focus toolview actions

Right now we have Show/Hide toolview actions which work great for
showing and hiding a toolview. However, one thing is missing:

How do I focus an already open (or closed) toolview quickly without
using mouse?

This change introduces yet another set of toolview actions which allow
you to focus a toolview quickly. This makes Kate more keyboard friendly
and allows you to do stuff like:
- Focus document pane and quickly switch to another document without
touching the mouse
- Focus project terminal or whatever is open in there

How it works:
- If the toolview is closed => open and focus it
- If the toolview is open => just focus it

After this change, in a follow up we should remove "Focus Terminal"
action from the Terminal plugin.