PLF-5843: Problem when using a custom jquery version

Problem analysis:
* Home page's portlets, login form, gadgets don't use the jquery version 1.7.1 defined in eXoResources.
  Each sub project uses different jquery versions (1.8.3, 1.7.2, 1.7.1, 1.6.2, 1.4.2) included by themselves.

Fix description:
* Use jquery 1.7.1 declared in eXoResources
* Delete other jquery libraries included inside gadgets or home page's portlets