Add a global context

[lizard-52]

Refactor the entire app to use the new GlobalContext class. The tag functionality even sorta works now!

Known issues:

• DB doesn't save item tags
• Can't delete tags
• Tag selection list is super broken and only works with arrow keys/enter

[lizard-52]

Global context looks good but navigation to the tag manager is really buggy

Can you elaborate?

[bpaul2]

When tring to add a tag to an item, it white screens for a second then places you on the ViewList activity where no buttons are clickable and the item that was suppose to be in the list is gone