(importing the graph advances in my branch)

[FIX] project view progressbars (2/2): the check time intervals were returned from the wrong django view function

- Graphes asynchrones testés en mode prod
- Documentation, README amélioré
- cosmetics: aération du code (en particulier bridgeness...)
- factorisation et meilleur positionnement de la fonction compute_graph

 Modifications qui seront validées :
	modifié :         README.md
	modifié :         bridgeness.py
	modifié :         cooccurrences.py
	modifié :         graph.py

[GRAPH] Now graph as json is saved according to its distance as key (needs to add bridgeness parameter as key).

[FIX] project view progressbars: add nDocs update and fix loop closure if several corpora are active

[FEAT] project view: show in real time the progression of active corpora workflow progressbars (use status API at regular increasing intervals 10 times, then stop trying, parameters are configurable)

[temporary FIX] import ngramlists: add a timeout message to say that the import is going on in background

ngrams reindexing: add timer (diagnostic: my functionis too slow, negative effect on list importing and free annotation add)

docs view: prepare feature for remote search in abstracts (will be useful when we do abstract indexing in sql etc)

(adds the new 'source' names that were formerly known as 'journal')

[FIX] server cache clean after detached instance error (should make the exception not critical anymore)

[FEAT] new param 'hyperdata_filter' for the main nodes API (ex: api/nodes?types[]=DOCUMENT&fields[]=hyperdata&hyperdata_filter[]=title)