Allow custom holdRepeat settings

[Geokureli]

1. Field to set the default holdRepeat initial wait and repeat time for a FlxControl instance

• Should be exported via mappings serialization

2. Ability to use any various different values without stomping on each other
   example:

if (controls.holdRepeat.custom(10, 0.1).DOWN) tortoise.x ++; // 10s initial wait, 0.1s repeat
if (controls.holdRepeat.custom( 1, 0.5).DOWN)     hare.x ++; //  1s initial wait, 0.5s repeat