Support podcast video upload from iOS devices

In the podcast element users can upload a video for each episode. The supported video format is mainly mp4 (flv for historic reason only, but not recommendet).

iOS for strange reasons did not switch to mp4 video, it still uploads MOV when using the camcorder in the Safari browser. But actually, the MOV is an mp4 file, it can just be renamed and everything works.

This issue is about fixing this problem:

• In iOS videos can be uploaded using the camera
• Detection of landscape / portrait mode and pre-filling of width and height