Add Upload Theme Repository

[sminnee]

Andrew, we'd like to you improve the theme repository on www.silverstripe.com

In short, we want registered forum members to be able to upload themes.

• They should be able to upload the theme as a .tar.gz file, with an image upload for the preview. Instructions about the filesystem structure will need to be provided.

• Ideally, you would want to some kind of validation of the uploaded .tar.gz to check that it's going to work with our system - check for .ss files, appropriate directory structure, no executables

• There needs to be an approval process, where someone at SilverStripe? approves a theme before it appears on the site.

• There should be a place that lists the themes that the current user has submitted, with an option to replace the theme with an upgrade. A version number field should be provided in the meta-data to facilitate this.

• Instructions for installation may need to be updated to reflect the new theme system.

Get this all working on http://test.silverstripe.com/ssopen/ - we'll launch it with the 2.1.0 release.

[sminnee]

Added note about approval process.