WIP: set up code coverage for Travis CI.
Reformatted lines in `CodeCoverage.cmake`.
Chmoded 644 `CodeCoverage.cmake`.
MAINT: simplified comment about build type.
Renamed variables for improved readability.
Unit-tested drawing methods in PaintingWindow.
FIX: corrected PaintingWindow::drawText().
FIX: corrected sending of Qt signals.
MAINT: Refactored unit testing for PaintingWindow.
FIX: added testing stub for PaintingWindow events.
MAINT: simplified unit-test-program-names.
FIX: added the right executable name to add_test.
Merge pull request #41 from DO-CV/maint-simplify-unit-test-program-names

[MAINT] Simplify unit test program names.
Merge remote-tracking branch 'origin' into test-painting-window
Merge remote-tracking branch 'origin' into maint-cmakelists-txt
Merge pull request #42 from DO-CV/maint-cmakelists-txt

[MAINT] Add possibility to choose build types in `CMakeLists.txt`.
FIX: fixed unit test for mouse move events.
MAINT: reformatted lines of codes.
MAINT: code cosmetics.
Added more unit tests for mouse and keyboard events.

N.B.: this will likely fail in Travis CI.