solve some problems of css for the create content page (modifications in forms.py and ldtform.css) publishedprojectslist.html : modification to have a valid link to the embed page

modifications to have relative src for media in the xml ldt of a project. - Migration in order to set all the project ldt with the new values in the xml. If the media has a content that doesn't exist, the media is erased. If the project has no valid media, the project is deleted. There is a test in project_tests. - The migration uses the command : set_projectldtiri - The command set_projectldtiri uses the function in utils relative_src_xml that returns an xml. The command deletes the projects that have no ldt or the ldt isn't valid (empty string) - Modifications in lignesdetemps to have absolute urls in the xml when we open a project or in the research when we display the results in lignes de temps

Starting 'modifications_relative_ldtxml' branch

start integration of chunked_upload in create content