Added tags to scene elements
Added "Add Action" Action
This solves issue #56. Apparently, a previous commit changed sceneElementActor and broke the setRenderer method, making that it always restored the initial renderer.
I've also added a test so this will not happen again :)

Note: I've implemented a "reflection-based" implementation of the equals method that may be interesting for other tests...
Simplified tags processing. Now, tags are recursively searched, instead of cached in initialization
The whole ChangeRendererActionTest has been reworked!
- Now, it relies on Apache's EqualsBuilder to determine equality among renderers (common-lang has been daded to engine's pom so we can use it in the future)
- It does not use json anymore for testing
These images are not needed
Merge pull request #54 from anserran/tags

Wonderful. Nice piece of code. Merging.
Added tags to scene elements and an "Add Action" action
Merge pull request #58 from jtorrente/issue56-changerenderer

This solves issue #56. Apparently, a previous commit changed sceneElemen...
Merge branch 'master' of https://github.com/e-ucm/ead into renderer-frameanimation