[TECHNICAL] Changes in transfers-related code

There are several things to find out and some others to improve regarding transfers. Here we can list and discuss everything related with that.

THINGS TO FIND OUT:

• Is a temporal copy (in .../tmp/...) created for every type of upload? (from content URI, from system)
• Why are there 2 different types of upload in case a temporal copy is always made?
• In the case of uploads from content URI, when is the temporal copy removed?

THINGS TO IMPROVE:

• Create 2 different fields in database for transfers: sourceLocation, which can be a content URI or a path, whatever is the case, and tmpPath, which is the path where the temporal files used for uploads are located. If a temporal copy is always made, both should be always not null (at least once they get copied, which can be before the creation of the transfer object)
• TransferDao functions can use @Update or @Upsert instead of @Query
• RemoveSourceFileWorker shouldn't receive a content URI as parameter, it can be a path as well. And the key variable (KEY_PARAM_CONTENT_URI currently) should be located in the worker itself

TASKS

• Research (if needed)
• Create branch feature/feature_name
• Development tasks
  • Implement whatever
  • ...
  • Implement unit tests (if needed)
• Code review and apply changes requested
• Design test plan
• QA
• Merge branch feature/feature_name into master

Start by tracing the two upload types and determining when temporary copies are created and removed. Then inspect TransferDao and RemoveSourceFileWorker against the proposed sourceLocation and tmpPath fields and parameter changes. Done means the transfer model and related operations are updated, with the required unit tests and QA plan addressed.