Screenshot updates to tutorials

[rosiel]

Purpose / why

In a recent commit to the Starter site, we changed the node form, so that Model (required field) is now at the top. I changed the two tutorials and their embedded screenshots to reflect the new form. While I was in there, I made minor edits to wording.

What changes were made?

• Screenshots updated
• Screenshots that were jpg are now png (and what a difference in quality!)
• Changes to "Create a resource node" and "How to create a collection" to reflect this, and just clean up the wording and alt text a little. No major content changes were done.

Verification

Check for grammar and verify the images work.

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?

[ajstanley]

Tested locally. It all does what it's meant to.