Add Popover CSS component
Realign pointer element to centre of trigger
Add .sg-block selector

To allow better styling of sections on the styleguide. Also removes
_popover selectors
Remove redundant :before/:after
Abstract z-index into placeholders
Reposition pointers
Tidy up Styleguide
Fix missing alert boxes on Styleguide
Reorganise z-indexing on popover
Add new .menu styles

As per design
Change the popover to use CSS triangles

As the rotated squares overlap content within
Add :focus state to menu
Adds hideOnBlur to Styleguide example
Fix syntax errors
Remove unncessary parameter in centerAlignTargetToTrigger
Merge pull request #55 from moneyadviceservice/popover-component

Add Popover and Option Menu components