feat(popoverTriggerDirective): allow declarative popover control
feat(popoverTriggerDirective): support custom events for triggering popover
refactor(popoverDirective): rename id to popover-id

Attribute usage between popovers and popover triggers should be consistent.
feat(popoverTriggerDirective): default popoverId to parent popover
Merge pull request #4 from rackerlabs/popover-trigger

Popover Trigger