Merge pull request #65 from the0ne/master

get rid of the annoying empty screen

updated by android studio

updated to latest gradle

Fix crash when api is already busy: Skip updating list

Fix keeping list position after update

Fix using the front camera when set in preferences

Fix missing close of main menu when starting qr code scan

Fix missing icon for add item by qr code

Added option to rename and delete a selected item

Added option to add item by scanning a qr code (needs backend support)

Raised compile SDK and build tools version

Change front camera selection and use a checkbox

Option to hide checked items

Menu access to cached list, save checkmarks in cached list