Create a browser ballot screen

[fossfreedom]

Web-browsers are a personal choice - lets find a user friendly way to allow users to choose which browser should be their default.

If necessary, add the corresponding repo.

Browsers should include

Firefox (standard repo)
chromium-browser (standard repo)
Chrome
Vivaldi
Opera

Only criterial here is that the ballot screen should only show browsers that have a debian repo, repo's for the version of ubuntu and most importantly are actively updated. i.e. would rule out - for example - midori which is rarely/never updated in the standard repositories.

Possibly add the ballot screen to the proposed welcome screen - https://bugs.launchpad.net/budgie-remix/+bug/1564634