Create input event in the stack.

Since we are using `qApp->notify`.
Fixed duplicate signals.
emit `event->buttons()` instead of `event->button()`.
Reactivate test keyboard and mouse input in Travis CI.
Replaced `QTest` functions by manual event sending.
Remove unused include file.
Merge pull request #51 from DO-CV/fix-keyboard-mouse-input-tests

[MAINT] Fix keyboard mouse input tests.