Propostal: add support for automated testing

[ruimaciel]

Guitar's issue tracker includes a couple of issues which justify adding unit and integration tests to prevent regressions. (See #117 , #108 ) Adding unit tests to Guitar with QTest is trivial, as shown in this commit.

However, in order to cover individual components with tests (unit, UI, intregration, etc), it's necessary to subject Guitar to an extensive amount of refactoring, not only to get the projects to actually support tests (i.e., qmake and its subdirs-based project structure) but also to peel out testable components that can be tested in isolation and enhance their testability.

As this requires a significant volume of work, it's important to get a green light from the project maintainers to ensure that this would be aligned with the project goals.

So, what are your thoughts on refactoring Guitar to add support for automated testing? @soramimi please chime in. I'd love to hear your thoughts on this potential workfront.