Settings

Hi
See pull request - "Add subcategories to reports #8"
I'm trying to do something about it. First I would like to modify settings.
See your comment:
"This patch needs to be split into smaller bits, e.g. first split out the refactoring to pass the settings object to TimeLog/TimeWindow/Reports classes (but ditch the setter methods -- provide a mock class in the tests)."

setter methods - for various tests it's required to have settings set properly. Either by setters or by whole configuration.
provide mock class - don't really get it / not sure whether this is required

In this pull request I modified Settings class and single test "doctest_TimeWindow_reread_no_file".
Settings allows set config file in init method and there is flag whether this file is required - at least for tests it is.
Directory src/tests will contain required configs for various tests. 

If this form is OK, I will modify other tests and related classes - TimeLog/TimeWindow/Reports.