BuildFailureScanner: import failed tests as failure causes
Add configuration options for test result parsing

Make the parsing of failed test cases optional (default disabled).
Allow the user to specify to which categories the failure causes should
be assigned.
Test result parsing: fix unit tests

The addition of new configuration objects in config.jelly requires an
update of the unit tests. This fixes errors like:

    JSONObject["testResultParsingEnabled"] is not a Boolean.
Test result parsing: don't make configuration variables static

Make sure the configuration variables are non-static, as commented by
rsandell.
Test result parsing: do not add to statistics

Do not add failure causes originating from failed test cases to the
statistics, to avoid problems due to these causes not being present in
the known causes database.
Test result parsing: put configuration descriptions in separate keys

Instead of placing long descriptions directly in config.jelly,
especially when there are parentheses (and associated escaping)
involved, use a key and place the actual description in
config.properties.
Test result parsing: set default list of categories to empty

When writing tests for the test result parsing feature, not explicitly
specifying any categories would cause a null pointer exception.
Instead of expecting each test case to specify a (possibly empty)
category list, do this in the actual implementation code.
Test result parsing: add unit tests

Add some unit tests to cover the newly added test result parsing
functionality. This requires two new setters in PluginImpl.
Merge pull request #25 from patrickdepinguin/testresult

Allow importing failed tests as failure causes