Add commit preparation hook to downloads of contributing section

OME-DCO-1.1-Signed-off-by: Sebastien Besson <seb.besson@gmail.com> (github: sbesson)
Fix header of commit preparation hook

OME-DCO-1.1-Signed-off-by: Sebastien Besson <seb.besson@gmail.com> (github: sbesson)
Add section to CONTRIBUTING.md about signing and hooks

OME-DCO-1.1-Signed-off-by: Sebastien Besson <seb.besson@gmail.com> (github: sbesson)
Fix CONTRIBUTING.md

OME-DCO-1.1-Signed-off-by: Sebastien Besson <seb.besson@gmail.com> (github: sbesson)
Rename to hook to append .hook

OME-DCO-1.1-Signed-off-by: Sebastien Besson <seb.besson@gmail.com> (github: sbesson)
Add section about the DCO to the source code page

OME-DCO-1.1-Signed-off-by: Sebastien Besson <seb.besson@gmail.com> (github: sbesson)
Americanize and fix get->Git

OME-DCO-1.1-Signed-off-by: Sebastien Besson <seb.besson@gmail.com> (github: sbesson)
Use user.name/user.email for DCO signed-off-by

OME-DCO-1.1-Signed-off-by: Sebastien Besson <seb.besson@gmail.com> (github: sbesson)
Insert OMERO sidebar template after page TOC sidebar

OME-DCO-1.1-Signed-off-by: Sebastien Besson <seb.besson@gmail.com> (github: sbesson)
Reformatting VA docs to make less intimidating!
Merge pull request #846 from hflynn/rebased/develop/sidebartoc_order

Insert OMERO sidebar template after page TOC sidebar (rebased onto develop)
Merge pull request #849 from hflynn/rebased/develop/VM-doc

Reformatting VA docs to make them less scary  (rebased onto develop)
adding session engine section to sysadmin docs
giving more links to the Django doc
replacing prerequisites by the link to Django doc
links distinction
fixing spelling mistakes
adding Django clearing-the-session-store link
removing space
adding SESSION_EXPIRE_AT_BROWSER_CLOSE and SESSION_COOKIE_AGE