Update committers list & add link to wiki

[ysuarez]

Purpose / why

There are currently two lists of committers and emeritus committers:
https://islandora.github.io/documentation/contributing/committers
https://github.com/Islandora/islandora-community/wiki/Islandora-Committers

This PR is an attempt to end up with a single list, which would be easier to maintain.

What changes were made?

• I made sure that the github.io version of the lists had the same information as the wiki version of the lists.
• I also added a link to the wiki committers page.
• I made one committer an emeritus committer, as alerted by @seth-shaw-asu (Debbie Flitner)
• I again alphabetized both lists

Verification

Interested Parties

• @Islandora/documentation
• @Islandora/committers

Checklist

Pull-request Reviewer

Pull-request reviewer should ensure the following:

• Does this PR link to related issues?
• Does the proposed documentation align with the Islandora Documentation Style Guide?
• Are the changes accurate, useful, free of typos, etc?

Person Merging

The person merging should ensure the following:

• Does mkdocs still build successfully? (This is indicated by TravisCI passing. To test locally, and see warnings, see How To Build Documentation.)
• If pages are renamed or removed, have all internal links to those pages been fixed?
• If pages are added, have they been linked to or placed in the menu?
• Did the PR receive at least one approval from a committer, and all issues raised have been addressed?