* test/api/*.vala: Renamed files that contained mock objects to *-mock.vala,
not *-test.vala.
* test/testcase.vala: Renamed to test-case.vala for consistency, remove
TestCase class from Gee package since that's really not true. Clean up
code for consistency.
* test/meson.build, test/CMakeLists.txt: Split TestCase compilation out
into a separate test lib.
* test/client/application/geary-configuration-test.vala: New unit test
for Configuration class.
* test/main.vala: Add new unit test to the client suite, ensure the
memory GSettings backend is used as the default so we get default
setting values, and never save any changes made.
* test/CMakeLists.txt: Add new unit test source.
* src/client/application/geary-config.vala: Tidy up code a bit to adhere
to code conventions.
