Add missing config for web development server in Linux walkthrough
Update instructions for 12.04 and onwards

- Add instructions to install OpenJDK 7 on recent platforms
- Add Ubuntu versions to liblzo installation note
Fix various stylistic markups to align them with doc policies
Align OSX/Linux walkthrough structures
Fix indentation throughout the page and minor markup
Add Ice 3.4 to the list of supported Ice versions for 12.04
Unify development server sections of both walkthroughs
Move developer section to a standalone document included in the walkthroughs
Fix default Ice version for Ubuntu
Create installing from source chapter and split Using Git section

Move Git page to checkout the code and build system to the new chapter
Add references to the Linux & OS X waltkthroughs
Fix links to source code page
Fix introductory paragraph of Installing OMERO from source chapter
Update OSX configuration used to test the Homebrew installation
Add reference to dev doc in the walkthroughs Development server section
Fix order of Debian from newest to oldest
Add link to source code page in Using Git and fix GitHub spelling
Edit fixes suggested by Helen
Fix Linux installation walkthrough as suggested by Helen
Merge pull request #309 from sbesson/rebased/develop/walkthrough_fixes

Walkthrough fixes (rebased onto develop)
Minor fixes and increasing consistency in sysadmin docs.