Popover is not being removed when initiator element is removed from DOM

[lugovsky]

Issue type

I'm submitting a ... (check one with "x")

• bug report
• feature request

Issue description

Current behavior:

Currently if Popover initiator element is placed in the modal, for example, and modal is being closed, popover stays visible and not hides itself alongside with the modal.

Expected behavior:

It should be hidden and removed from DOM alongside with the modal.

Steps to reproduce:

Put button in the modal which opens popover. Make popover display on click. Open modal, open popover, the close modal. Popover will stay visible.

Angular, Nebular
Nebular RC.7, Angular 5.X