Create Developers top level menu

This introduces a new top-level "Developers" menu. It takes the following from the Athena menu:

• all of the material in the "Athena developers" sub-menu of Athena
• the Git workflow (including the Git tutorial underneath it)
• IDE integration

Other menus are left alone, with the exception that the "Software infrastructure" menu is renamed "Shifts and infrastructure".

Other changes:

• the ordering of the items in the developers' menu is slightly changed
• the persistency section of the developers' tutorial is moved to its correct place
• an evidently orphaned part of the Git tutorial is reunited with the rest of the material (see #47 (closed))

Closes #47 (closed).

These changes look good to me.

I do not like that the URLs do not match the navigation, but I guess we gave up on that again

While we are still doing the redirects then I think it's too much hassle to fix. In the meeting yesterday James suggested having a "flat" directory structure make things consistent at least.

mentioned in merge request !88 (merged)

added 1 commit

• 99a8cc90 - Capitalising first letter of titles

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resolved all threads

added 8 commits

• 99a8cc90...dda0c465 - 6 commits from branch main
• e127b714 - Create Developers top level menu
• 359510e2 - Capitalising first letter of titles

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changed the description

merged

mentioned in commit 8b213905