The main changes are:
* Split RuleCreator: move some of its content to RspecRepo and to
RuleEditor in new modules.
* Refactor tests accordingly.
Other less important changes:
* Sort and remove unnecessary imports
* Remove unimplemented functions and unnecessary classes
* Make some functions private
* Move pushd from utils to tests where it is only used
* Reduce code duplication here and there
* Remove unnecessary Mock in some tests
* Improve coverage for add_language_to_rule
* Generate description and metadata for rules with no language, so that they get indexed.
* Index rules with different types in language specializations.
* Improve validation to reject new rules with no language specialization (i.e. only a predefined set of such rules is allowed because they were imported from Jira and kept for historical purposes).
* Write smaller JSON files, reduce their size by 30%.
* Improve test coverage of CLI application.
