tests: split sqlb-unittests

Instead of a single executable running different unit tests at the
same time, split the sqlobjects and import parts out of it.
While this currently duplicates the cmake boilerplate for each,
it allows to finetune each properly (like build only the sources for
it, in the future), and to call each separately.

Add the QTEST_MAIN in each test, and remove the manual QCoreApplication
handling in TestImport (handled by QTEST_MAIN).

src/tests/testsqlobjects.cpp

@@ -3,6 +3,8 @@
 
 #include <QtTest/QtTest>
 
+QTEST_APPLESS_MAIN(TestTable)
+
 using namespace sqlb;
 
 void TestTable::sqlOutput()