Add merge buttons to the show pages for mergeable objects

[gjvoosten]

Details pages for mergeable objects now show a button for an admin to directly go to the merge page for that object.

Closes AB#1163

User changes

• None.

Superuser changes

• None.

Admin changes

• An admin can now click a button at the top of the page for an organization, position, person or location, to go directly to the merge page for that object.

System admin changes

• anet.yml or anet-dictionary.yml needs change
• db needs migration
• documentation has changed
• graphql schema has changed

Checklist

• Described the user behavior in PR body
• Referenced/updated all related issues
• commits follow a repo#issue: Title title format and these 7 rules
• commits have a clean history, otherwise PR may be squash-merged
• Added and/or updated unit tests
• Added and/or updated e2e tests
• Added and/or updated data migrations
• Updated documentation
• Resolved all build errors and warnings
• Opened debt issues for anything not resolved here

[midmarch]

Awesome !