Task:Download client for extras-applications

Idea
The client should be used in addition to the native application manager and provide easily more information for the inexperienced user. The client will:


 * ease finding and sorting applications based on different criteria (ratings, number of downloads, categories, etc.)
 * search for applications with a free-text search
 * get basic information about the applications (like description, number of downloads, ratings, comments, screenshots, etc.)
 * send feedback (like ratings, comments)
 * download the installation file and pass it directly to the application manager, which handles the installation

Server communication
The back-end implementation is ongoing work ATM. It is based on the open collaboration services API. The implementation doesn't apply in all parts to the standard, but the work is ongoing and the goal is to change and improve it step by step. More information about this you find in the /REST-API REST API.