Draft: Add horizontal Molex KK 254 and its fork, aka KF2510

See kicad-footprint-generator#676 for description.

This is not meant to be merged, but to be finalized before starting to work on generator. The fake part has the "holder" on a different side than Molex (Molex has it on top, fake has it on the bottom).

Questions:

• How to name the fake part?
• What should be changed on the silkscreen?
• I don't know how to calculate the courtyard. It could be smaller, but similar parts use a larger one.
• What datasheet to quote for the fake part?
• It probably make sense to draw all the visible (but only visible) parts of pins?
• It would probably make sense to have an additional version for placing the connector at the edge of the board (can be taken care of later)?
• The size of the female is know and it could be helpful to include it in courtyard, but no other connector does that.

Horizontal Molex:

Horizontal Molex fork:

Vertical Molex fork (almost the same as vertical Molex, but pin assignments are reversed and using 1.0 instead of 1.19 mm hole):

original: