feat(popover): added variation of popover with html unsave capabilities

Hi,

Some people (including me) needed a popover, which is able to use html unsave content.
I implemented it in the same way, the tooltip-html-unsave was done.
Extended the documentation and also copied and adopted the test a bit. This could be better for sure, but it test the same functionality, like on the standard popover.

regards,
Andreas