Add filter in order to allow devs to customize the community activity trigger list.

[thesquaremedia]

There is the ability to add parent triggers through the badgeos main filters. UI/UX wise it's better to add custom community triggers inside the community activity trigger. For instance a custom reply to specific forum trigger. unless of course you guys would prefer for me to add that functionality as a PR to the main plugin but in the meantime I created a PR including the filter change #66 .