add opt --active to profile list

[artivis]

Add --active option to profile list in order to print only the active profile with or without formatting (--unformatted).

$ catkin profile list --active 
- default (active)
$ catkin profile list --active -u
default

[NikolausDemmel]

LGTM.

I have a slight preference to not use the shortcut -a here. This doens't seem to me something for regular use from the command line but rather from scripting.

[artivis]

Hi, thanks for the feedback.
Indeed my first use case is scripting, shall I remove the -a option ??

[wjwwood]

@artivis please do remove the -a flag. I think this is good to go otherwise.

[artivis]

Shortcut removed, doc updated.