Switch to app storage

[rkdarst]

• Instead of using sdcard storage, is it possible to put all data in app storage, so that it is removed when the app is uninstalled.
• Upstream wanted it to stay on the sdcard so it would stay after the app was removed... which is not necessary when using webservice and not good for long-term studies.
• The disadvantage is that it doesn't allow plugins to write to the same data, so this should be configurable somehow.

[rkdarst]

I have code for this - waiting for upstream merge to put the actual change in our main branch.