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
Point server-upgrade at jvm_memory_settings
Implement feedback from PR
Remove adaptive strategy
Merge 'origin/dev_5_0' into 12311-auto-memory
merge dev_5_0 -D org: PR 819 (12311 auto memory docs)
merge dev_5_0 -D org: PR 836 (Managed repository template path expansions)
merge dev_5_0 -D org: PR 852 (Tidy Upgrade page incl. Paris requests for 5.0.3)
merge dev_5_0 -D org: PR 853 (Document orphaned datasets/plates retrieval via getProjects/getScreens)
merge dev_5_0 -D org: PR 855 (Session engine (rebased onto dev_5_0))