Online repository.

Added online repository functionality.
TODO,
When importing the online element to a scene, download it's resources(if they weren't already donloaded) and copy them to "/images" folder.

Process:

1) We download the content of a file [elements.json](http://repo-justusevim.rhcloud.com/elements.json) from a server I created.
If the content of that file isn't the same as the one we have in memory then we proceed to recreate the UI with the downloaded info.

2) We download the [thumbnails.zip](http://repo-justusevim.rhcloud.com/thumbnails.zip) and unzip them, Those contain the thumbnails for all the elements that appear in [elements.json](http://repo-justusevim.rhcloud.com/elements.json) plus a "bindings.properties" file which specifies which thumbnail image (value, only .png suported) has to be bound with which element/model entity (key, must be the element's title used as an unique identifier). Those thumbnails are then loaded and displayed in the gallery.

There is room for a lot of improvements, e.g. showing notification messages to the user or even a progress bar.