Allow configuration of target frame for apps/links

[bubblesnout]

I use my Homarr dashboard as my home page and new tab page in Firefox, This is only achievable in Firefox via an add-on as Firefox does not allow you to set a custom new tab page by default, however Firefox has an issue where addons are not able to clear the browsers address bar so I lose the ability to type in the new address bar as soon as I open a new tab.

The following add-on works around this by placing the page in an iFrame: https://addons.mozilla.org/en-US/firefox/addon/custom-new-tab-page/

Unfortunately links from inside an iFrame don't work correctly, as the developer states on the add-on page the best thing to do is have all links open with a target of "_top" however in Homarr we don't have control of this - only the ability to open in a new tab. It would be a pretty simple change to add the ability to either specify a custom target per-app or choose from the list of standard targets (_blank, _self, _parent, _top).