Delete SandBox files on app start

and added reasons in Config.h why we don't wait for apps to close or
delete files at another time.
Simply, Editable (Direct) opening
General clean-up and bugfixing
Fixed stupid bug that prevented previewing of MHT files.
Finally fixed BOTH htm and mht file preview

Previous commit broke normal html file previewing.
Added frame for local html previewer
Initial Implementation of OpenWithDialog