[mod] update TODO
[mod] exercice should also store the answers
[enh] display tests of a lesson on the lesson page
[enh] start to move test interface on lesson to angular
[enh] add more stuff into form to add test on lesson page
[enh] get tests from database on lesson page
[enh] can add a new test in full ajax
[enh] update list of tests on the page if adding a new test is successful
[enh] clean name field when adding a new test
[mod] also send skills data to angular view in lesson page
[enh] record when the test has been created
[mod] default ordering for tests
[enh] continue ui to add skills for the test
[mod] change test creation submit button
[enh] bind value of select to ng-model
[fix] make 2 buttons of form working independently
[enh] form allow to add a list of skills to test
[enh] add required skills in the backend
[enh] make it impossible to create a test with an empty name
[enh] display skills that needs to be tested