Updated snapshot pages

[snoyberg]

Follow up from #49.

We haven't fleshed out everything we want to do yet, so we should plan on adding items to the description. Here's what we know so far:

Info:

• Recommended installation will be to use cabal.config. We'll have URLs like the following:
  • /lts/cabal.config for latest LTS release
  • /lts/2/cabal.config for latest LTS in the 2 series
  • /lts/2.3/cabal.config for LTS 2.3 specificly
  • /nightly/cabal.config for latest nightly
  • /nightly/2014-12-11/cabal.config for the nightly from December 11, 2014.
• The remote-repo links will still work, but they will be secondary to the cabal.config method. They will now function as the exclusive snapshots do today. Result is that we'll end up with just one version of each snapshot, and different installation instructions whether you want exclusive or inclusive behavior. (And inclusive will be our default.)
• I've updated the snapshot pages already to have a link to a listing of all packages in a snapshot, including doc links. Perhaps that should go on the snapshot page itself.

TODO on the snapshot page:

• cabal.config view and download links (?download=true)
• All packages listed inline (Michael will do)
• Remove metadata, packages and haddocks links
• Collapse top bar/banner
• Title/publish date
• Bundle link moved to bottom
• Explanation of how to get started: download cabal.config, optionally remove old database, cabal install