Add navigation items for every label + refactor editing labels

[Crustack]

Closes #49

• Labels are now listed in the navigation view, to directly view notes of a specific label
• The amount of labels displayed is limited to 10, if there are more than 10 Labels another navigation menu item with "X more" is displayed to indicate it
• Refactored the Labels View to show proper Edit/Delete buttons instead of relying on Long Click menu to popup, which I find unintuitive
• Moved the App version text to the bottom of the Settings Fragment