Column Squidge!

Columns now squidge together if there is a gap, can be toggled with the
prop_columnSquidge property.

Tweaks to make the game more exciting (based on playing whilst testing):
* no score when tapping on a gem
* gain big scores when clicking the button
* gain some time when completing a link
* infinite play up to maximum size of 7x7
* less harsh score penalty for single link (and no added time for
single links)