installer should delete Issues.ocf, Experimental.ocf etc on install (part of solution to #1029)

(cherry picked from commit ba2d71c94251b4bbbb146d2018040654b64e54c0)
fix update via *.ocu on Windows 7 (#870)

see bugtracker entry for details

(cherry picked from commit 325d2b80e1a8ccb3c55a98000de75cd167f1ce19)
Moved Dialogue to Helpers.ocd to avoid copies
Fix issues with Crash.ocs intro (#951)