[JENKINS-24398] Support for Token Macro Plugin in description

Supports to expansion of macros provided via the token macro plugin.
Macros are expanded only if no regex is given.
I see two options here:
1. Make the dependency to the Token Macro plugin mandatory
2. Add a check if the plugin is installed.

I actually propose option 1 as this is the most convenient option for the user as in this case the Token Macro plugin is automatically installed if missing.

Let me know your thoughts.