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.
Merge branch 'master' of https://github.com/e-ucm/ead into styled-text
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)
Merge branch 'master' of https://github.com/e-ucm/ead into styled-text
Integrating comments from @anserran:
- CallbackWrapper refactored to SimpleLoaderParameters
- assets.resolve(String) and FileHandle.exists not used to check if a file exists (this is done by loader and serializers)
Merge pull request #79 from jtorrente/styled-text

Styled text
libgdx doesn't support opengl es 1.x, and the api changed
engine-html is constantly broken by libgdx, so we'll deal with that when we have to, not before.
Merge branch 'master' of https://github.com/e-ucm/ead into Galleries