Improve developer contributing page(s)

[hflynn]

New 'Working with OMERO' single page introduction and 'Contributing to OMERO' section under 'Introduction' to replace old 'Development Processes' section at the bottom of the page.

Remaining issues:

• Promote these sections better, particularly to make sure importance of 'Contributing...' section is clear.
• Add pages/sections to Contributing covering - how to document a PR properly, more info for 3rd parties on getting their PRs reviewed and accepted
• Fix writing-test.txt re: Eclipse files
• Add documentation to testing.txt about omero.rootpass
• update Developer Standards page

[jmoore]

Helen: not sure of how to move forward on this, but happy to discuss. Suggested changes about moving things upwards are certainly fine.

[hflynn]

OMERO.clients needs at least a minor re-write if only to remove the link to itself and change the file name.
A brain storm on re-ordering the index might be helpful at some point. I think the development process should definitely be nearer the top and maybe some of the pages within this section could do with clearer titles.