Split the VpCore struct into the local and global part.

This makes the way to have global configs that are loaded on application start
an local settings that are kept for every window/tab.
Implemented prefix aware history searching (#7).

If ':set' is already typed in the inputbox, the history will only step over
those items that matches this prefix. Now vimp behave a little bit more like
the great vim editor.
Save the commands together with the prefix ':' in history (#7).

This is not so flexible, but makes many tings easier to implement to violate
the concerns of the components.