Some refactoring on mdrender
Improving coverage of mdrender to 100%
Adding render_and_extract function to mdrender service
Flake8 corrections
Removing list_of_milestones from project api
Pytest mutable object fixture.

Usage:
        def test_something(object):
            # mutate object as needed
Creating reusable "filter_by_tags" function.

Moving the filtering-by-tag logic out of TagsFilter into a reusable function.
Turning off signals dispatch when testing units

Model signals pre_save and post_save will be turned off when running
unit tests because they are interfering with the tests.
Automatically skip slow tests

You can mark a test as slow using:

    @pytest.mark.slow
    def test_something():
        ...

Use the option "--runslow" to tell the test runner to also include slow
tests:
        py.test --runslow ...
Moving neighbors logic into standalone module
Change travis configuration to use the new tests system
Fix requirements
Fix tests
Fix tests (II)
Improved a little the history freezers and values registers api
WIP:
WIP
WIP: splitted history mixin.
WIP: services and mixins.
WIP: