Made use of ng2-bootstrap-modal.

Made use of ng2-bootstrap-modal.

This will remove all the duplicate code of ng-bootstrap popup.

Made following changes to the below files,

1. app.module.ts:
	a. added the confirm modal component to declarations and entryComponents section because component will be created dynamically.
	b. imported BootstrapModalModule from ng2-bootstrap-modal
2. vnfs.module.ts:
	a. removed the confirm modal component from declarations and
	   entryComponents section as it is already declared as part of
	   app.module.ts.
3. confirm.component.ts:
	a. added two more varibles 'cancelButtonText' and
	   'confirmButtonText' to ConfirmModel interface. these values will
	    be sent by the caller code and the button lables will be set
	    dynamically.
	b. implemented cancel method that sets the modal result value to
	   false, this is called on click of close
	   button.
4. about.component.ts:
	a. Made use of confirm.component.ts.
	b. on click of 'view change log' buton we are calling open()
	   method which inturn opens the confirm modal component.
5. about.component.html:
	a. Removed call to versionLogFile() method as this method is
	   called from open() method.
	b. Removed the ng-template code of ng-bootstrap which is no more
	   required.

Issue-ID: APPC-1088
Change-Id: I9de545debed145ef35e31807acd1e9bd9cc2bad4
Signed-off-by: Arundathi Patil <arundpil@in.ibm.com>