merge branch 'custom-lessons'

And with that, there is an easy way again to train on self-supplied
texts in KTouch. This fills the biggest remaining feature regression
in comparison to KTouch 1.x, only in a much improved way.

Instead of providing a simple file dialog to pick a text and use
that immediately, we organize the custom lessons in a special
course so the user can track his progress on these lessons like
for the built-in courses. Also the custom lessons are kept separately
for each user profile and keyboard layout.

In the editor for custom lessons, a much simplified form of the full
blown course editor, we offer the usual quality checks. This is
important, so the user has a chance to identify characters he can't
type with his keyboard before he actually hits them during training.

DIGEST: