This doesn't fix a bug but remove some tricky code. The shift key is no
longer different when the "double tap for capslock" option is on.
The handling of the option is moved to Pointer instead and becomes
simpler.
Layout modifying functions are removed from Config to LayoutModifier as
static classes.
The two classes are (weakly) mutually dependent, the refactoring is
purely for the purpose of making shorter classes.
The only change is that 'modify_numpad' is changed to remove duplicated
code. This has the side effect of making the "double tap for caps lock"
option affect the shift key in the numpad.
