🎉 Complete UI rewrite to use webpack

Using webpack

This allows us to extract the UI JS into individual modules.

Show better errors when send to server fails

This update also fixes #72 and now the plugin shows different errors depending on the response from github (server) when sending tokens.
Details about the errors was added to the readme error section

Even though it is a major update due to the code change, it should not break anything in the code export part.