Preliminary version of an improved painting system

Another attempt to fix xournalpp/xournalpp#41.
It should also resolve xournalpp/xournalpp#82
This is not quite as polished as it should be,
but it should given an impression of whether or
not the painting is performed sufficiently fast.
On my system the time to paint is generally
between 0.1 and 1 ms and there is no noticeable
delay.

So far the shape recognizer is not yet integrated.