Switching active tabs based on .tabs

Switching active tabs based on .tabs, not on the parent of the current t...ab, therefore also useable with a list; as discussed in https://github.com/thomasf1/Framework7/commit/eece04e10e6285201633188fb5c35b1de7527960

I think this is a more elegant way of doing things, as the parent could include non-tabs with a class active; or as in my case the parent isn´t the right scope.