Enabling suggestions for @-mentions in groups component

https://buddypress.trac.wordpress.org/ticket/5934 : To enable suggestions specifically for group forums - once the required script gets loaded for groups component -, .bp-suggestions needs to be added.
Merge pull request #3 from MarkyMarkNo1/patch-1

Add support for @mentions suggestions in parts of the Groups component.

Further work is required in core before this will work, but this will get BP-Default ready.
See https://buddypress.trac.wordpress.org/ticket/5934

Props MarkyMarkNo1 (m@rk).