Tweaked empty and filled box images to horizontally align black circle.
Merge remote-tracking branch 'upstream/master'
Merge pull request #26 from martinjbaker/master

Revised box images
Boxes are now centred within the view. Previously box count multiplied by 71.0 was used which made the box view 10pts wider than it really is, leaving more gap on the right than the left.
Merge branch 'master' of https://github.com/aporat/KKPasscodeLock
Merge pull request #27 from martinjbaker/master

Make 4 boxes horizontally centred in the view