refactor(core): beginning of directive tests

Reformatting gulpfile, preparing tests
adding proper dependencies
test(ui): adding some tests

Tests, but need to reset the whole document to prevent duplicates of
the markdown elements.
test(core): working tests

Adding the afterEach to clean the previous generated markup, tests
passing.
[Warn] Failing test, wrong logic
[Warn] testint tests
test(core): much cleaner structure for tests, adding some

Entierely refactor the test environnement which was a little dirty,
Adding some tests, proceeding to test the editor other functionalities
test(markdown): adding some test for basic markup

Adding tests about the markup of the following components:
-code blocks
-image
-numbered list
-simple child lists
-headings
-separator
refactor(tests): moving resetContent

Moving the reset of the content inserted in the document for future implementation
of the tests that will allow to change the markup easily
Merge branch 'feature/tests' into develop