SourceMap: Independent of settings.

The aim is to make source-map generation
independent of WE's "generate .map" settings
for LESS and SCSS..

It will compile just once on document open (which
it already does); if the map generation is set,
read from the generated map file. Otherwise,
in compiler parameter we set path to temp file,
read all text and delete the file.
Margin: Corrections for Go To Defninition.

In scenarios like sel1 > sel2 + sel3,
the CSS parser attach `+` and `>` signs to the
previous selector, while CSS source map count it
with the current node (SimpleSelector; that is
part of selector).
Merge pull request #833 from am11/sourcemap-improvement

SourceMap: Independent of settings.