Adds custom target for OverlayPanel #942

[steineggerroland]

Fixes #942

Adds the second parameter target to OverlayPanel.show which is already documented in https://primefaces.org/primevue/showcase/#/overlaypanel and addressed by issue #942.

Citing the documentation:
target: Optional target if event.target should not be used

Here is probably still an issue, because the code uses event.currentTarget and not event.target as stated in the documentation.

[cagataycivici]

Fixed on our side, thx. Still I think event.currentTarget is required, otherwise problems occur like overlay panel aligning it to an icon in the button, not the button itself.