Use current host as default when adding new trigger dependency.

Steps to reproduce:
1. Open trigger edit or create form.
2. Open trigger list for another host in another tab.
3. Select "Dependencies" tab and click "Add" for trigger form opened at step 1.
Result: Popup window default host filter is set to host where triggers list being viewed.
Expected result: Popup window default host and group filters are set according to trigger selected at step 1.

MOVED from ZBX-6669 (5)