enh/unify "Default:" strings

I am not sure if that is worth for 0.8.x series, but on the other hand we already disturbed it a lot (i.e. modified lots of "config" files), so it might actually be the right moment.  

I have fixed fail2ban.conf for the actual default values code assumes.  But now the question is either we should simply completely remove those in action.d/*conf files where they pretty much duplicate the actual value specified underneath and/or leave only in few spots where they point to actual defaults of the actual 'action' command, although they are useless there per se since usually those are intended to be used with an cmdline option (e.g. ```-p <protocol>```) thus leaving them empty would result in incorrect cmdline.

Another question, while at it, what should be our convention here:

```Values: CMD``` vs ```Values: [ CMD ]``` or simply allow both types happen there is only a single choice. ATM we are using both conventions across files