Implemented MFR RedNet support.

As discussed in IRC here's my shot at implementing MFR's RedNet API for the redstone conduits.
Tested with MFR latest (and without) and it works well in both directions as far as I can tell.

A few remarks:
* If there are "cycles" (i.e. two connections between a conduit network and a RedNet cable network), signals will stay high even if the original source dies. This state is *stable* however, i.e. it has no performance overhead, at least not as far as I can tell, so I think this is acceptable (also, I don't know what could be done about this, realistically). It's kind of like two repeaters operating at infinite speed ;-)
* ~~The API will be shipped as it is now. If this is not desirable, some `Optional` interfaces would have to be added. This way, however, it can work even if MFR is not present, which seems preferable. The main problem with this is, that the MFR/RedNet API does not use an API annotation, so other mods cannot check for it directly (meaning they'll probably check for MFR, meaning it'll only work if MFR is also present).~~ API is not being shipped, MFR has to be present for this functionality to be available.
* I am not 100% sure about the use of `canConnectToExternal` in `BlockConduitBundle` line 878 (in particular the `ignoreConnectionMode` parameter). It seems to work fine, but some confirmation that this is correct would be nice.