Apply changes to all configs

Fix up ABL - Add PROBE_Y_FIRST option. Arduino 1.6.8 required.

K8400 has 1xXY an 2xZ endstop plugs

Rigidboard differs a little in configuration from the PrinterBoardRevF we modeled the code after.

About Configuration.h:
・Fix the PR #4899 (ABL: Enable by type. Bilinear for all.)
Remove Duplicated contents

・Fix the PR #4305 (Custom boot screen feature improvement)
Revert from "during boot" to "during bootup" in all the example
Configuration.h

・Fix the PR #4207 (Clean up, simplify and generalize the Allen-key-probe
code.)
Resolve and relocate the duplicated definitions in Z_PROBE_ALLEN_KEY
section

・Follow-up the PR #4805 (Additional documentation of Configuration.h)
Add forgotten changes to all the example Configuration.h

Adjust spacing

About Configuration_adv.h:
Add missing description of SLOWDOWN for DELTA

Adjust spacing

- Extrapolate properly for even numbered grid points
- Extrapolate using average, not median
- Improve bilinear grid report output
- Add debug output for bilinear extrapolation
- Add option to extrapolate from edge, not center

ABL: Enable by type. Bilinear for all.

Define status LED pins without condition

Include requirements in "Implemented Codes"

Fix HEATERS_PARALLEL