feat(collapse): makes collapse to support two-way binding or hide exposed function(toggle,hide,show)

[mkjeff]

  @ViewChild(Collapse)
  private collapse: Collapse;

  toggleMenuItem(menuItem){
      // change by directive, instead model, the state of binding source will become inconsistent 
      this.collapse.hide(); 
  }

[valorkin]

There are isOpen property

[mkjeff]

there is no isOpen property in collapse.component.ts. could you point out the specific file?

[valorkin]

not isOpen, sorry, check how it works at demo page:

https://github.com/valor-software/ng2-bootstrap/blob/master/demo/components/collapse/collapse-demo.html#L5