less: we should be consistent with diffstat-ish colors

With this change, on the changeset page, the 'change counters' for the whole
changeset (in the top right corner) use the same colors as the counters for the
lines (a little bit below) and the line change highlighting.

- move .changed from kallithea.less to kallithea-diff.less
- be more generic with selectors in kallithea-diff
- remove remaining style from kallithea.less