Debug launcher

[julianseeger]

(depends on https://github.com/Qabel/qabel-desktop/pull/551)

gradle setup as it should be (at minimum).

• extracted guiTest into it's own module to allow for gradle default behavior src/main and src/test
• added debugLauncher module to launch a client with debug options (ScenicView for example)
• fixed README

As a bonus, IDEA can now use the actual gradle modules deactivate because the source sets are the expected gradle defaults (as described above)

Because of the new modules, the build targets have changed. Previously, the tests could be run with

./gradlew test            # unit tests
./gradlew guiTest         # gui tests

now, both modules rely on the default test target and the global test executes both:

./gradlew test            # unit AND gui tests
./gradlew :client:test    # unit tests
./gradlew :guiTests:test  #guiTests

(the : in front of the module name is optional but I like it do distinct between modules and targets quicker)

As a result, the second gocd stage will fail because there is no task guiTest anymore, but if the first stage succeeds, that means the guiTests have already been executed.

[julianseeger]

this now depends on the already merged https://github.com/Qabel/qabel-desktop/pull/544 (metaVolumes PR)