Working with text styles
Merge branch 'master' of https://github.com/e-ucm/ead into styled-text
Merge branch 'master' of https://github.com/e-ucm/ead into styled-text

Conflicts:
	engine/core/src/main/java/es/eucm/ead/engine/renderers/TextEngineObject.java
Merge branch 'master' of https://github.com/e-ucm/ead into styled-text
Basic implementation of text styles. Roughly speaking, all text attributes related to how it is rendered (scale, font, color) have been encapsulated into the TextStyle wrapper.

The style of a Text object can be defined directly into the object or through a reference to a file. This allows rapidly changing the appearance of all the text in a game, in one shot, but also personalizing the attributes for a particular piece of text.

Text style is optional. If not set, a basic white, 1.0F style is used.
Added new galleries system. The galleries extends BaseGallery.java
Added filter tags panel
Merge branch 'master' of https://github.com/e-ucm/ead into styled-text
Added capability to associated views with context menues
- Context menues will be shown when the user right clicks the context
menu owner.
Small fix in lefrgithlayout
Added TopBottom layout, analogous to LeftRight layout
Added ActionOnDownListener
Convenient method for AbstractWidget
General context menues are set opaque by views
Convenient method to add loaded assets to assets
Context menu can be opaque
Merge branch 'master' of github.com:e-ucm/ead
Reviewing serializers and loaders (not only texts but all of them). Many serializers and loaders have been deleted and replaced by generic ones that avoid repeating code.

SceneElementSerializer has not been edited. We should decide on what to do with this in the near future (I'll open a different issue)
Updated editor android project.properties to API 15
Game view now draws scene limits