major rework on the misdn / input plugin side

Hi!

I was trying to get the data model right for the TRAU mux/demux handling, and discovered it is about time to re-do the entire 'input' side, i.e. the interface towards the actual E1 link.

The main objectives are: 1) ability to deal with multiple BTS on one E1 link 2) ability to easily integrate E1 drivers != mISDN, e.g. zaptel while still keeping most of the E1 related functionality in common code 3) ability to easily add things like Abis over IP later

So please stay tuned for some potentially quite big committs in that area during the next couple of days.