Added a style manager page to manage available and default styles in geoserver.

Added a style manager page to manage available and default styles in geoserver. This lets the user configure styles already available in the geoserver for use on their geonode layers. This was previously only possible by doing it in the geoserver admin ui and doing updatelayers or forcing a save on an individual layer. 

Adds a new jquery plugin that will be handled by bower shortly.

@ingenieroariel can you review and comment/pull?