Add qualified name tests specification (see #118)

Augment 'tests' option of 'rebar eunit' command with ability to specify
tests to run using module-qualified names. This change also forced me
to change the way modules for coverage and for testing itself are
selected - module-qualified tests specifications are now taken into
consideration. Extend tests to cover new functionality. Update
dialyzer_reference accordingly.
Merge pull request #119 from deadok22/qualified-test-spec

Add qualified name tests specification (see #118)