[Website] Add page summarizing project contributions since project inception

[asfimport]

We have already been doing this on a per-release basis, e.g.

http://arrow.apache.org/release/0.10.0.html

Reporter: Wes McKinney / @wesm

_{Note: This issue was originally created as ARROW-3077. Please see the migration documentation for further details.}

[asfimport]

Wes McKinney / @wesm:
Note ASF best practices regarding recognizing corporate contributions https://www.apache.org/foundation/marks/linking