Automatically Generate SQL Result String if not given

Description

In issue #1 (closed) we added support for SQL Coderunner questions via moodle-tools. However, adding SQL Coderunner questions requires manually inserting the exact result string into the YAML file that is used to generate the XML Coderunner file for ISIS. In this issue, we aim to extend this functionality by allowing to leave out the testcase-result field in the YAML file. This will trigger a query to the given database (currently 'eshop' or 'uni') and fetch the correct result string and add it to the generated XML file.

Todo

• enable leaving out the 'result' field for 'testcase's
• if the 'result' field is left out for a 'testcase' we automatically fetch the result from the database given by the mandatory database field in the YAML file
• we add the optional column-width field for SQL queries