Allow template-sets to be installed

[maybeec]

As an architect, I want to define the set of template-sets to be initially installed on each developers machine so that my team can start working right ahead without needing to cope with cobigen initialization routines first manually.

Acceptance Criteria

• I am able to configure in the cobigen configuration template-sets to be preinstalled by the configuration key template-sets.installed
• I am able to specify comma separated maven coordinates (e.g. groupId:artifactId:version) of my template-sets to be installed
• core should install configured template-sets on startup if not yet installed or adapted
• All configuration is documented in the wiki and finally also occurs on the website

[maybeec]

Hey team! Please add your planning poker estimate with ZenHub @GuentherJulian @LarsReinken @mdukhan