workflows: revamp testsuite
- Implements a renewed testsuite for workflows with better coverage overall.
- Moves the workflows and widgets loading to use registry. Tests also use their own test registry.
- Test specific workflows are now moved to the testsuite.
- Cleans up the tests a bit, renaming and moving the tests in test_halt into the renewed test_workflows suite.
- Makes the tests visible for the overall invenio testsuite by adding the TEST_SUITE variable.
- Fixes an issue with the custom Log handler and inheritance.
Signed-off-by: Jan Aage Lavik <jan.age.lavik@cern.ch>