Reuse dot_clk input as externel reset input

[niclashoyer]

This changes reuse the dot_clk input on rev 0.2x PCBs to sense the /RESET line of the C64. With this the TeensyROM gets back into the menu when an internal reset is fired in the C64 (e.g. another reset button or other devices like blue64). The trace from dot_clk to U4 needs to be cut and a jumper wire from RESET to the right pin on U4.

@SensoriumEmbedded I removed the whole DbgFab0_3plus ifdef block, because I just built for 0.2c, but I think the whole thing could maybe be put behind another ifdef block, so one could switch at compile time.

Currently I'm still testing this. I observed two race conditions / edge cases:

• RESET does not bring back the menu (C64 BASIC is loading) (about 1 of 30 resets)
• Starting a CRT file goes straight back into menu (about 1 of 3-5 times)