OMHD-398: Refactor OmhFile for better support of folders

[damiann5f]

Summary

I created a brand new branch as it was faster to re-refactor than to spot bugs & resolve build issues & conflicts in https://github.com/openmobilehub/android-omh-storage/pull/14

Demo

n/a

Checklist:

• [x] Documentation is up to date to reflect these changes
• [x] Created Unit tests

Closes: OMHD-398