Add a "transfer/copy data" function

Related issue: https://github.com/MuntashirAkon/AppManager/issues/138

**Situations:**

Situation 1:
- User uses a FOSS app
- User decides to modify and compile the app by themselves from source
- User installs modified app
- There are two apps, one with previous data, one without
- User now needs to transfer the data, while making sure the permissions are changed automatically — tedious for lots of data

Situation 2:
- User uses AM to "clone" an app (e.g. create an app named App-copy)
- There are two apps, one with previous data, one without
- User now needs to transfer the data, while making sure the permissions are changed automatically — tedious for lots of data

**Solution:**
It would be nice if AM provided a function that could transfer/copy the user data from one app to another, while making sure the permissions are changed accordingly. A warning should also be shown that such operations should only be conducted between different versions/builds/flavours of an app, not between completely different apps.