Adding styles for standardising radio buttons and checkboxes

• Add the new styles
• Tweak button styles because labels are now floated
• Add contains floats to to list of buttons

Js code and gemfile updates can be found in smart answers

https://www.agileplannerapp.com/boards/105200/cards/5197
update gemfile to latest toolkit version
Scope selectable class to label to reduce possible class name clash
Remove clear both and display block, as now not required.
Include js for radio and checkboxes in static as appose to in
separate repos

https://www.agileplannerapp.com/boards/105200/cards/5197
Scope js to label.selectable to match the css scoping
Merge pull request #449 from alphagov/styles-for-standardising-radiobutton-checkboxes

Styles for standardising radiobutton checkboxes