Fixed #36, refactoring

- #36 asset paths have now type Path and are relative to asset
directories (not complete paths)
- relative paths are shown in GUI for texture tasks
- renamed paths in class AssetTask
- saved tasks deleted (not compatible with new AssetTask)
- some refactoring in gmm.service.assets
Merge branch 'master' of https://github.com/Katharsas/GMM

Conflicts:
	src/main/webapp/WEB-INF/tags/tasks_lists.tag