Fixed a bug in the calculator

Fixed a bug in the calculator where decimal places were being stripped
during calculation.
The new tab URL has a trailing slash
Improved checkboxes in the getting started guide

The checkboxes now have to be limited and widgets that require
permissions (just Recently Closed for now) shouldn't be shown, the
defaults were also out of date.
Added a function to remove iFrames onbeforeunload
Merge remote-tracking branch 'origin/master' into New-Tab