Merge wip development branch to master

Still needs to be merged:

• Implemented token authentication and REST account registration (6d8cc6ab)
• extensions: rewritten application (0f169be4)
• extensions: added license field to extension version model (f681af8a)
• extensions: search: fixed API endpoint (97b26889)

Changes needed:

• Extension.rated and Extension.rating fields should be updated with new ratings