Migrate from webview to native UI

[divadsn]

To-do List:

• Tickets overview
• Account page
• Pricing list
• Webview for buying new tickets only

This will also allow the app to run offline thanks to the introduced account sync in 0f2d71c

[divadsn]

Tickets overview and account page to be done in ticket-overview branch.

[divadsn]

ticket-overview branch will be renamed to new-ui and webview will be removed entirely.

New tickets should be purchased using a desktop device for various reasons.