Use EIFFEL_LIBRARY environment variable instead of EWF_HOME and CJ_HOME

The goal is to reduce the need to many per-project environment variable
(such as GOBO, EPOSIX, ...).
This was discussed on the mailing list before :
https://groups.google.com/forum/#!topic/eiffelhub/sheBaxKAMtk
Merge branch 'master' into eiffel_library_env

Conflicts:
	graphviz_server.ecf
Merge pull request #5 from oligot/eiffel_library_env

Use EIFFEL_LIBRARY environment variable instead of EWF_HOME and CJ_HOME