describe repository template path expansions
add further clarification to template path rules
add some template expansion examples
clarify behavior of %subdirs%
suggestions from @jburel
suggestions from or inspired by @pwalczysko
clarification suggested by @manics
suggestions from @pwalczysko and @ximenesuk
Document orphaned datasets/plates retrieval via getProjects/getScreens

OME-DCO-1.1-Signed-off-by: Sebastien Besson <seb.besson@gmail.com> (github: sbesson)
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
adding clearsessions to the windows doc
Merge pull request #836 from mtbc/managed-repository-template-path-expansions

Managed repository template path expansions
Merge pull request #855 from aleksandra-tarkowska/rebased/dev_5_0/session_engine

Session engine (rebased onto dev_5_0)