Major refactoring : allow the plug-ins to present their own factories.\n\nThis allows us to put the Process interface in the Scenario plug-in, and the Inspector interface in the Inspector plugin
Update .travis.yml

No need to make install anymore. 

ToDo : make Experimental; make cppcheck
Move plugin-specific files and interfaces in their respective plug-ins
Re-enable inspector
Fix tests running
Merge and fix tests
Merge branch 'master' of https://github.com/OSSIA/i-score into refactor/plugin_factories
Enable testing on travis