fix regression caused by #606

If WHISPER_DIR is specified w/o a trailing slash all metrics will contain a
leading period. This patch makes sure any leading period is removed from the
metric name.

See #606 for more details.
Revert "Add a function "sortByName""

This reverts commit fc74d347a178c670ef58d6090670c890eaf0ba8a from #419

Revert, since this is a duplicate of d7ae284 from #522
upgrade fix as suggested by @brutasse
Merge pull request #662 from ImmobilienScout24/fix/regression/build_index

fix regression caused by #606
Merge pull request #663 from ImmobilienScout24/revert/419

Revert "Add a function "sortByName""
configure NullHandlers in case logging is not requested

We frequently see error messages of the form:

[Tue Nov 12 01:06:53 2013] [error] No handlers could be found for logger "cache"

This commit fixes that issue.
reconfigure the metricAccessHandler

Make it have a backup of 1 file, like all the other Rotators. Also, this logger
isn't even used anywhere, so it will not matter.
introduce a function to configure loggers
configure infoLogger via function
configure exceptionLogger via function
configure cacheLogger via function
configure renderingLogger metricAccessLogger via function
make log rotation configurable
fix import
midnight should be a string
adding test file for logger
improve tests

Test various aspects of the logger module.
add docstrings to the unit-tests
update comment
check that deactivation of log file rotation works