Switch to extending from OsmApi.

Waiting for https://josm.openstreetmap.de/ticket/9744 to get merged in.
Make plugin depend on a newer version of JOSM

The newer version has a method exposed that we need to fix the https problem
Removing obsolete wording in plugin description
Initializing API after creating it

Without this the version number isn't set and requests fail.
Merge pull request #19 from iandees/extend-osmapi-class

Switch to extending from OsmApi

This will allow using https for API requests.