Adds a list templates command to the command line interface.

Adds a ```list-templates``` command to the available commands. Also contains misc clean up/improvements of command files.

Refactors out template related code into its own object. The ideas behind this is to reuse the template related methods direct from ```ActivatorLauncher```. Can be refactored further but was unsure how far to take it in this PR. Suggestions are welcome.