Add basic highlighting test case
main-widget: Remove widget placeholder
user-list-entry: fix margin-right usage
AccountCreateWidget: Force creating a new proxy

If the proxy has already been defined, only one call to request_token
succeeds, all subsequent calls fail with the usual "unauthorized" error
AccountCreateWidget: Don't get stuck after the first try

We were unfortunately not resetting the sensitivity of the fields if the
first try did not work.
MainWindow: Implement the 'add new account' list entry
main-window: Add a frame to the listbox
Update POTFILES.skip
tests/highlighting: Also test tag type