slight wiki reorganisation

[Duncan Coutts]

I've reorganised the front page of the wiki and some of the subpages.

I've tried to organise it by audience:

      * General audience and users
      * People who maintain platform packages
      * Distro packaging people
      * Release team

For example the distro people and package maintainers want to know about
the release timetable etc.

I've moved the main planning pages for the release team to a
major-version specific page:
http://trac.haskell.org/haskell-platform/wiki/2009.2

This has a copy of the minor release schedule along with lists of things
to consider for upcomming minor releases.

When we get into the mode for the next major release we'll open a new
page for that release series to track which new packages and versions
will go in etc.

Hope this looks ok, point out anything that's missing or obviously
silly.

Duncan