yet another abc to ease the dashboard development

[coh2]

At this time (2012-Mar-2), the dashboard [1] only supports the sqlite3 backend through some rather ugly means (raw sql queries).

By adding another abc and inheriting the backends from that one also, one can simply import that abc, run the configure and have a simple means of supporting virtually every backend (with the exception of the text one).

The abc would only need one or two abstract methods. And by splitting it into a different abc instead of extending the backend abc, someone with a custom backend won't have the burden of implementing those methods if there's no need for them.

[1] https://github.com/coh2/pastycake_dashboard