Move to own test file and refactor view_blame_file tests
    Blame view tests had identical content on all their branch|tags so our tests were not valid since
    we could not determinate from wich ref the content was coming. The 404 errors could be due to different
    reasons and that was not properly tested neither.
    
    This commits moves the blame tests to their own test file, dissect them on many small tests, uses different
    content for each branch|tag and properly tests the different 404 cases