- Exports the contexts, addons, JS configuration (including
  GEOR_custom.js) into the datadir
- Makes the rest of the webapp configurable outside of the webapp WAR
  (using the same mechanisms as previously)
- Allows mapfishapp to be easily customized by server-side addons (it
  allows automatic scanning of jars which classes begin with
  org.georchestra.mapfishapp.addons)

As the other PR, it requires the introduction of the georchestra-module.

Fixing path to the addons in the webapp when no georchestra.datadir is
provided.

Changing maintainer name/email to PSC

See comment here:
#1038 (comment)

Tests: Utests adapted, tested at runtime with jetty:run (with and
without datadir option).

Sync GEOR_custom.js with the one provided by the template configuration.

s/config//

Do not check too early if the addon is activated or not, check it at the
very end of the process.

This allows to deactivate addons provided by default in mapfishapp,
simply by copying it into the datadir and explicitely setting it as
disabled in the config.json spec.

- Hardenning tests when trying to find files on the FS
- Aslo allows to set images from different formats (JPEG) for context
  capions.

Tests: utests added for NPE avoidance
runtime tests for the context captions

Now using the controller systematically, irregardless if
georchestra.datadir is configured or not. Getting the relevant file in
both cases (like it is done for other controllers).