Adapt to new sharing API in SFOS 4.4.0 / Steps to create a new `sfos4.4` release branch

[Olf0]

When the "download on demand (DoD)" build targets for SFOS 4.4.0 are available at the SailfishOS-OBS, do:

1. Revert PR .desktop file: Trivially bail out of SailJail #250.
2. Create a new sfos4.4 branch from the sfos4.2 branch? See also Update, below.
3. When proper documentation for the new (again!) sharing API is available, implement it.
   For the source code (changes) of it, see Split transfer and sharing plugins sailfishos/transfer-engine#6
4. Concurrently to point 3 issue Define, implement and test a proper SailJail "profile" (plus evaluate its necessity) #236 shall be addressed (which includes step 1 above).

Update: pvourela's (a sailor) newest info sounds as if the sharing API introduced with SFOS 4.2 will remain. Hence step 2 listed above might be superfluous and all this can be implemented in the extant sfos4.2 branch.

Update 2: A few posts in the FSO-thread "Examples for sharing api" may be helpful.