Include funders' logos on last page

[Gemmamysoc]

We don't name our funders at the moment, but we probably should. They are:

• Omidyar Network
• The Indigo Trust
• Open Society Foundations
• The William and Flora Hewlett Foundation
• Making All Voices Count
• Microsoft
• The Joseph Rowntree Reform Trust
• Google.org
• Bytemark

[zarino]

Closed by https://github.com/mysociety/annual-report/commit/bce53f68548826c3fbcf1449203da85d0d6712f6