- working on getting storage (browser/localstorage + dropbox) working
 * moved connectors folder back out of core ( keeping in line with how exporters and editors are not part of the core)
 * DropBox connector : added correct imports, wrapped in intermediary class, and made modular
 * the integration of connectors with the main app is now similar to how exporters are handled : a mapping (connector name ->connector object) of connectors
get instanciated in the app and is passed to the main menu, which dynamically generated UI entries for the different connectors
 * preliminary integration of dropbox within that system is in, loging in to dropbox works

- working on /refactoring projectBrowser / library/ persistance (functionnal and ui): nothing concrete yet, but will benefit from all of the above

- added additional test for project, to verify if the "dirty" flag is set correctly (when adding new files to the project, changing files etc)
- various smaller cleanups in main app
- a few improvements for the dropbox connector:
* clearer visual indication of signed in/out status
* correct handling of login/logout commands & events