Compile & Min LESS when output files don't exist

Was having trouble with my team - we don't commit compiled or minified LESS to source control. When working individually on projects, we'd have to open all LESS files and use the save listener to re-create the .min.css and .css files in order for the LESS compilation to kick in and start checking these on build.

I think Issue #14 describes similar problems (although I didn't experience the crash).

There did seem to be some explicit checking for not compiling in these conditions (CanCompile function, Lines 41-49) so these changes may be unacceptable if there's a scenario I haven't considered here.