Re-organise sponsor listings, adding financial sponsors per core discussion.

Re-organise sponsor listings, adding financial sponsors per core discussion.

Moving forwards we'll have three types of sponsors:

- Contributing - those that the sponsor team are responsible for.
- Financial - those who donate to an NPO.
- Servers - those who provide servers/infrastructure.

For the financial sponsors, there are a few rules:

- "NPO" means a recognised NPO, (which includes SPI and PGCA).
- Each NPO may choose whether or not to list any sponsors on this page.
- Each NPO may define the criteria under which sponsors are listed, and
  any levels they wish to use.
- Conference/event sponsorship does not count; it must be sponsorship of the
  organisation itself.
- Sponsors may be listed once under each NPO they have donated to.

Note that the same sponsor may be listed in any or all of the categories
(contributing, financial, servers).

Patch by myself and Jonathan.