Changed gitignore to ignore the compiled lib.

If the library is compiled in the false way, this won't mess up the repo
anymore.
Added an Checkable class.

The new widget type is for checkboxes.
Added a setChecked() function to the Checkable.
Added the virtual draw() function to the Checkable.
Started working on the checkbox class.
Forgot to write the empty implmentation of draw() in the Checkable
class.
Worked on the notifications queue.