keypad: Set some default row and column spacing
Some default spacing was given in the demo but not in the widget, this ensures the keypad will look decent by default.
Fixes #76 (closed)
@bertob the values in the demo used to be 8 for rows and 10 for columns, here they are 6 and 6, can you check the values are right?
Note: changing the default value can be considered an API break so it's before Saturday. :x