Extract alternative/absolute layout as placeholder

Sass placeholder selectors allow us to easily apply this layout mode
with other page/per-Controller classes.

Signed-off-by: Alex Coles <alex@alexbcoles.com>
Reference absolute layout selector w/tidier syntax

This does not change the compiled output, but keeps properties grouped
in a way that (arguably) makes for better readability.

See: http://sass-lang.com/documentation/file.SASS_REFERENCE.html#parent-selector

Signed-off-by: Alex Coles <alex@alexbcoles.com>
Fix width of work package view o/s project context

Signed-off-by: Alex Coles <alex@alexbcoles.com>
Move work package layout styles to correct file

Signed-off-by: Alex Coles <alex@alexbcoles.com>
Specify min-height for work packages split view