Add possibility set text and use builtin tinymce icons in custom buttons

Conflicts:
	.gitignore
Updated jQuery lib
Added locale converter. This resolves #129.

Conflicts:
	Twig/Extension/StfalconTinymceExtension.php
Added asset[] parsing to custom_css

The problem which this Commit refers to is described in
https://github.com/stfalcon/TinymceBundle/issues/110

Problem: It was not possible to use the asset[] method inside a
custom_css path for theming of the tiny-mce editor content.

Fix: The tinymceInit() now parses the config for custom_css for themes
through the getAssetsUrl() function therefore replacing asset[] urls
defined in custom_css of a template to working relative urls
Support multiple assets in custom_css parsing
Fixed documentation regarding custom_css in themes