Ability to add LABELS to each ticket

Inspiration is coming from github issues repository and this same Damn bugs' userecho issues list.

Could be useful that each user could add one or more labels to each tickets, in order to group and categorize each one. Then clicking on each one, could become a way to apply custom filters.

In my opinion, default labels names could be ok, but should be important that users could create new ones (at least who with Account manager role)