Up to date config changes to support FelixPrinters

The default config is for a Felix 3.0 with single extruder.
Main changes are:
- PID enabled for the 3.0 heated bed in order to eliminate Z-ribbing due
to bed expansion/contraction (target temp 55C).
- "Babystepping" feature enabled during print for micro-adjustment of
Z-height during first layer print.
- SD card insertion signal is correct versus the current drop on the
FelixPrinters site which has this signal incorrectly inverted.
- All other recent Marlin fixes/features are available via config edits.

- If you have a dual extruder printer, feel free to make appropriate
edits and submit a pull request.