Media Source based gallery

I have updated the plugin to use the media source functionality of MODX instead of just using the filesystem.(defaults to filesystem - so no breaking changes).

A drop-in extra that allows the gallery to use a media source (for example S3, or cloud files). I have updated the uploaders and the file paths in the get() function to allow for urls at the start of filenames.

We are currently using this in production and have no issues.

When images are shown through the snippet the whole URL is given from the media source. So this allows the gallery to upload images to other locations.

Our use case is:

Websites are hosted on Rackspace web servers - however all user assets (images / uploads / etc) as uploaded to Cloud Files (CDN). This allows us to load balance sites without copying resources around (Server A and Server B).

However with the existing Gallery plugin we had an issue - that all images would get uploaded to Server A and would not exist on Server B. Adding Media Source capability to Gallery allows the admin to upload images to Server A - (then the media source uploads to Cloud Files) and the images are referenced from cdn.clientdomain.com.

So all images are viewable regardless of the originating server.

All the upload functions remain working within the Gallery (multi upload / etc)