Remove the Attica requirement by using the store's new links

This removes patch removes the hard requirement on Attica, but retains most of the functionality (minus the location magic and multiple links), by using the KDE Store's new abilities to link to profiles and avatars using the username of a person.

This adds a checkbox (similar to the one found in Kirigami.AboutPage as of kirigami!283 (merged)) which defaults to off, so we never go online to fetch stuff unless the user explicitly allows for this to happen. Future work might be to store this checkbox' state, perhaps in a global fashion.

An about dialog without this patch:

The same about dialog, with the checkbox checked:

The checkbox defaults to off, and the look is as above.

This is for the the https://phabricator.kde.org/T12198 task