Convert paste-kde to the new pastebin.kde.org API

The new API doesn't support using a name for the sender of the paste,
so this option has been taken out from the user.

Instead of using seconds, the new API uses minutes to expire pastes,
so the custom options has been changed to reflect that, maintaining
the same period of time (7 days).

The url has also been changed for the new API.
Bump version to v0.4