[WIP] 1.0 release

My PR integrating Propel became quite big as I kept pushing stuff not related to Propel, so I decided to reopen the PR under a new name.

I added a few new features, tried to solve a few problems and cleaned the code/tests. I think this could be the right moment to release a 1.0.0 version.

Here is a quick summary of what should be done for this new version:

- Propel related:
  - [x] integrate Propel (#175)
  - [ ] integrate Propel2
- [x] use the PropertyAccess component instead of Reflection to read/write in objects
- [x] implement the Xml metadata driver (#134)
- Namers related:
  - [x] make the file and directory Namers use PropertyMapping instances instead of using Reflection
  - [x] unify file and directory mapping interfaces for more consistency
  - [x] fix #126, #150, #161, #179 (still needs confirmation but should be fixed)
- [x] backport #106 event-listeners behavior
- [x] allow generating an image link without an entity (#131)
- [x] check that uploading several fields works (#35)
- [ ] last but not least, update documentation

Does anyone see other things to do?