Plugins reorganization

Hi the piwik team!

I reorganized all the plugins folders to respect this current pattern:

* /plugins/<PluginName>/images/
* /plugins/<PluginName>/javascripts/
* /plugins/<PluginName>/stylesheets/
* /plugins/<PluginName>/templates/

I also started to rename:

* The ambigous files, like misc.js, index.js, index.css, styles.css, etc.
* No starting upperCase for stylesheets files
* Starting upperCase for javascripts files that contains the declaration of an object

Finally, I fixed some remained links to theme/default.

Cheers,
Thomas.