Tentative of weigthed order for compression dict

See Google Doc for justification.
Tested.
Creation of another subproject for decomp. lib.

Creation of another sbt project for the decompression library.
Things such as the AstRecomposer and corresponding tests should be moved there
at some point.
Merge branch 'master' of https://github.com/aghosn/persistence
Moving of the decompression to the library folder

All in the title. NB: the library project depend on plugin