Multiple fixes to Valo theme

Multiple fixes to Valo theme

- Added initial Sass API for Accordion and TabSheet (previously only
one mixin)

- Renamed ‘darker-of’ function to ‘darkest-color’, which now supports
more than two colors

- Refactored notifications to use the new position classes as well as
the new animation-in/out functionality

- Refactored overlay styles to use animation-in/out functionality

- Fixed all unwanted white-space and scrollbar issues in all browsers
(font-size:0 or line-height:0 no longer necessary), and fixes vertical
centering in horizontal layout (#13671)

- Fixed borderless menubar clicking bug (Firefox and Opera)

- Fixed table column selector, which no longer produces scrollbars if
placed directly inside a scrollable area in full size

- Fixed table outline overflow in Opera (now using box-shadow instead
in all other browsers except IE8)

- Added toolbar support for windows (header and footer)

- Moved optional notification styles to common-stylenames.scss

-Various other small tweaks

Change-Id: I42343199be12f6d909b9584b7dce3e258846da81