Rewrite DCF77 module

[kbabioch]

The DCF77 module in its current form has a bunch of problems:

• There are a lot of reports of bad reception, quite possibly having to do with problems in the routines itself.
• The module is hard to maintain without messing something up, because of all the conditions. An implementation in form of a FSM would make much more sense.
• The log output is buggy as the same timings are being output multiple times, although nothing has changed internally.
• The log output is ugly and not that great to read as the lines get way to long.
• Receiver type detection is not necessary as this can be accommodated easily by either a software switch and/or simple hardware. All known receivers have an inverted output, anyway.