Lins which open as popup window must be underlined or styled as button

[chmst]

Steps to reproduce the issue

Links must be underlined.
If a weblink opens in a modal, the link is a button and not underlined

Expected result

The link, opening in a pop-up looks like a button or it is underlined

Actual result

System information (as much as possible)

Additional comments

[joomdonation]

@chmst Could you please make PR to solve this issue?

[chmst]

Please test #512