Redoing concatenation of compiled JSTs

Minor performance improvement, avoid memory relocation every time we
iterate and do a string concatenation. Instead add results to a list and
join them at the end.
Performance boost in BaseFinderStorage.find_storage

Avoid listing all files for every finder for finding a file. This is
actually a bottleneck when the directory hierarchy is nested or the
number of files served in DEBUG mode is big. Since this flow is done in
every request, it slows down page loading.

In production environments where templates are usually cached performance
doesn't get hit by this.
remove unusued match_location