Initial migration of in-place import docs

This is a copy of the ome-internal documentation
(InPlace.pdf and ImportScenarios.pdf) to the main
sphinx codebase. The changes required for the
migration were:

 * exclude `downloads` because of the *.txt ending
 * change `:omerodoc:` to `:doc:`
 * prepend a few slashes for absolute URLs

 Otherwise, the content has not (yet) been modified.
Better import scenarios introduction
Further title modifications
Add links to in-place-import
Rework in-place intro
Add proper reference links
Extend limitations section
Remove 'docs are not yet public' section
sysadmins: Merge server-install-linux into general server-installation section
Remove repetitive 'have' prefix
Fix bullet indent
Add ref link to dropbox section
Link to in-place from scenarios
Add future development section
server-installation: Drop leading ./ from bin paths
server-installation: Complete sentence
Plans, accounts & wording tidying
Add import files to what's new list
Fix missing '-' from file name!
removing part about session engine on windows