CONTRIB-4186 CSS Cleanup

This encloses the whole report into a new
.local_codechecker_results div and applies
such class to all the styles to avoid problems
(.region-content) with other parts of Moodle.

Some unused styles are also deleted and a bit of
extra space is added beween each reported problem
for better readability.
CONTRIB-4186 Calculations to lib, pass them to renderer.

This moves the calculation of totals to locallib,
for later improvements in the way they are shown
by the renderer by diferentiating error/warnings/good.