MapStore templates

This commit include all changes for the templates system for MapStore (see proposal page: https://github.com/geosolutions-it/MapStore/wiki/Proposal-%234:-Basic-MapStore-Templating-System)

* Allow header/footer customization. @tdipisa
* Allow to parse header and footer from the default configuration (static or remote) @tdipisa
* Manager Login changes
 * Read user logged information at startup
 * Logout for spring security
 * Uncomment error on maps grid load
 * Now if you're already logged on MapStore, the `login` state is applied.
* New Manager widgets
 * MSMTemplateComboBox
 * MSMTemplateGridPanel
 * MSMTemplateManager
 * MSMTemplatePanel
 * ExtendedHtmlEditor
 * ImagePicker
 * Plupload and image carousel utilities and dependencies
* Change the save/load maps behavior
 * New option `stateWhiteList` to set properties to be saved. Default list is `["sources", "map", "CSWCatalogues"]
* Categories initialization on mapstore
 * Add `TEMPLATE` category to the categories initialization for mapstore.

Also changes on `manager.html` and `composer.html` in order to allow the new load methods.

This commit requires also:

* geosolutions-it/GeoStore#68
* geosolutions-it/OpenSDI-Manager2#2

and is a squashed merge with templates branch.
Merge pull request #363 from alediator/templates_final

MapStore templates