Revamp website layout and content

I made a series of changes that would be quite painful to do in separate MRs, so here it is:

• Remove some old pages that were not linked from anywhere
• Remove contributing page, and instead link to the wiki
• Remove faq, roadmap, tips, vision pages
• Add about page, which condenses together some of the info from the deleted pages
• Remove the "community" category and replace it with the "contributing" category
• Fix up the mobile gear releases page and link to it from the header bar
• Add Fedora and Arch Linux to the "install" page
• Add some font weights to content
• Add some konqi pictures

@carlschwan @bshah

I'm not sure if I need to do some things to update translations.