Experimenting with 2 buttons to add files or to add media. But doesn't work that great, so will revert.
rollback
Working on creating the thumbnails. Created a few extra EZ methods: runOnMain so you can run code from a separate thread on the main one. Also created a toast message method to show a toast message according to given string resource. Furthermore, I modified the content manager to add items on a separate thread now (where we also create the thumbnails) TODO: do with rest of IO dependent methods.

Currently the thumbnails fail, but will look at it soon. Created error messages to be displayed in toasts when something goes wrong.