Make group check for commands

[iuriguilherme]

Group admins explicitly solicited for blocking /feedback on groups:

Gustavo, [14.05.17 18:51]
Bloqueia esse comando em grupos tbm

Thiago Augusto (Jumper), [14.05.17 18:51]
Ops acho q cliquei sem querer no feedback, se o admin apagar agradeço

Gustavo, [14.05.17 18:51]
Só no pv

Apart from /conv and /price, other commands should be enabled on groups IF someone set it to.

For now it should be settable by configParser or /admin, but in the future, by a group moderator. This last requirement would require more telepot docs reading.