Migrate technical content from ibex wiki

[Tom-Willemsen]

Migrates instrument details and technical/developer information over from IBEX wiki (not migrating project management-related information as it is unclear whether that even remains relevant).

This is preparatory work, before we decide what to do with the remaining project-management content on the IBEX wiki, and to make that subsequent migration easier.

Once this PR is merged, the following pages in IBEX/wiki should be deleted:

• ARGUS instrument details
• CHRONUS instrument details (I have checked that the existing version in the dev wiki is more up-to-date than the version in the IBEX wiki was)
• HIFI instrument details
• OFFSPEC instrument details
• PEARL instrument details (I have manually merged independent changes that were made to pages in both locations)
• DMS
• Eurotherms
• nGEM detector (I have checked that the existing version in the dev wiki is more up-to-date than the version in the IBEX wiki was)
• PGC
• SANS2D-equipment-images-and-gifs
• TwoTier Sample Changer
• ZOOM Sample stack

[rerpha]

Looks good. I think we should split the motor extensions page to be generic and instrument-specific but lets do that as another PR.