Generate qualified component names
Read import statements to help base class lookup

With this change doxyqml generates "using namespace" directives
for each namespace. Doxygen will use this information to resolve
fully qualified base classes for us.
Add comments to explain `find_qmldir_file()`
Update existing functional tests
Add functional tests for qualified names
Also find qmldir for relative paths

The find_qmldir_file() function failed when doxyqml was invoked with relative
paths: os.path.dirname() was returning an empty string once we reached the
current working directory.
Merge pull request #8 from hasselmm/qualified-names

Generate qualified component names