WIP: Documentation revamp

this brings some changes for the 0.10 bitmask release:

• remove oblivia, add colnodo.
• introduce optional javascript detection of the platform in the landing page; downloads bundle by default.
• make the icons in the install landing page download the bundles; add links for more detailed pages.
• greatly simplify bitmask/linux install page.
• separate debian/ubuntu install pages.
• add links to alternative install methods (pip, git).