Unify two download-runtime models in o.j.t.runtime.as.handler plugin

ASTools has an integration plugin for astools vs runtime. With runtime now living at the bottom of the stack, this plugin may no longer be useful.

The runtime wizard dialog cannot load any runtime.ui dialogs because there is no dependency between as.ui and runtime.ui. To add a dependency here would basically make o.j.t.runtime.as.handler to be useless. All the code there could easily be pushed into astools' other plugins.

This isn't a huge priority, but it is a little silly to have two models doing exactly the same thing.