Downloads: add download failure reasons

### [REQUIRED] Use case description
User has ran out of free space on his/her device. He/she starts download and after several retries gets status update with "unknown" failure reason.

### Proposed solution
Add FAILURE_REASON_INSUFFICIENT_FREE_SPACE to Download.FailureReason IntDef.

### Alternatives considered
If aforementioned solution is hard to implement, could you at least add support for minimum storage requirement in bytes for the download to proceed. (This might be even harder as currently you store the combination of requirement flags in an Int and there is no way to store extra data)