v1.3.0: Version 1.3.0

As announced, 1.3.0 is a small release after 1.3.rc0 containing small fixes, but also a few improvements.

What's new

• Updates to Dutch, Lithuanian and Vietnamese translations.
• Fix inability to submit in OutputOnly tasks.
• Don't recreate participations (and thus lose their submissions) when reimporting a contest.
• Remove a few short flags for some risky operations in scripts.
• Includes all the changes from 1.3.rc0: https://github.com/cms-dev/cms/wiki/CMS-1.3.rc0-RELEASE-NOTES