Instant upload: rename files on upload

Hi,
So, this is a draft implementation for #649. It's not fully tested yet, as it still have at least an issue (about which I have a question, hence this pull request.

I'm using `[Images|Video].Media.DATE_TAKEN` to allow the user to rename the file depending on the date the photo or video was taken. It's working fine when the device is online at the time the media is taken, but not when the device is offline and the media uploaded later.

In this specific case, `InstantUploadBroadcastReceiver.handleConnectivityAction` manages the uploading of the file which has not been sent yet. However, at that time, we only have the (local) file path. The mime type was needed here, but instead of using the media store to retrieve it, a simple map lookup with the file extension is made. Is there any reason to this, excepted the fact it's simpler for the mime type only? I'll need to use the media store here to be able to fetch the date the media was taken, I think. I don't really see any other way.

Thanks