recovery: Allow key to repeat on hold.

This implements the ability to hold a key and have it repeat.
This makes it possible to hold down the volume key to scroll
down to a file.

Enabling repeatable keys:

ro.cwm.enable_key_repeat=true

To control which keys can repeat, you can set this prop with
a list of key codes, like this:

ro.cwm.repeatable_keys=137,200,151,300

If you don't set ro.cwm.repeatable_keys only UP, DOWN, VOL UP
and VOL DOWN will be repeatable.

Patch-set 1:  First commit
Patch-set 2:  Re-worked a little
Patch-set 3:  Now uses system props.
Patch-set 4:  Fixed USB connection bug
Patch-set 5:  Compressed down a bit
Patch-set 6:  Fixed spacing derp
Patch-set 7:  Fix bug + increase speed
Patch-set 8:  Slow it down a tad
Patch-set 9:  Took care of inline comments
Patch-set 10: Added UP & DOWN to default repeatable keys
Patch-set 11: EV_REP compatibility + logic changes
Patch-set 12: EV_REP takes precedence
Patch-set 13: Fixed spacing derp
Patch-set 14: Fixed time overflow >_>
Patch-set 15: Remove a little whitespace
Patch-set 16: Removed *~
Patch-set 17: Reworked per koush's suggestion

Change-Id: I7c7ef035c89210212bf08f8aa97150222d948d0c