SocialSharing plugin wrapper fixed and extended

- Added the (most important) `share` function
- Renamed SMS phonenumber param to indicate you can pass multiple by separating by a comma
- Renamed all `image` params to `file`, because any file can be shared (or even a file array actually, most of the time)
- Fixed `shareViaEmail`, because it was an unadjusted copy-paste of `shareViaSMS`
- Added `shareVia`
- Added `canShareViaEmail`
- Fixed `canShareVia` (subject was missing)
- Removed some now obsolete TODO's/notes