Improve Import/Export/Duplicate

[khase]

Description:

Improvements

• Remove properties Whitelist, Accesskey and isActive for exported courses
• Improve name duplication detection (1. Duplicate -> 'name (copy)', 2. Duplicate -> 'name (copy 2)', 3. Duplicate -> 'name (copy 3)', ...)
• Automatically redirect to Duplicated course
• fix crash when a non existing Task is referenced

Known Issues:

NONE

[coveralls]

Coverage decreased (-0.4%) to 48.053% when pulling 68f1d70 on feature/42-import-export into 77b6219 on develop.

[coveralls]

Coverage decreased (-0.4%) to 48.053% when pulling 5ce7869 on feature/42-import-export into 398eea9 on develop.

[coveralls]

Coverage decreased (-0.4%) to 48.389% when pulling 95118e1 on feature/42-import-export into 12cd1eb on develop.