UP-4148 Update CONTRIBUTING.md

[apetro]

See UP-4148. This is a retry of PR #347 , differing from that in that this version does not include a change to the recommended branch naming convention.

Updates CONTRIBUTING.md to

• Emphasize the necessity of the Individual Contributor License Agreement (ICLA).
• Suggest communicating about proposed changes via uportal-dev@ and uportal-user@.
• Request that code consider style conventions and uPortal architecture.
• Suggest sharing and collaborating in a public feature branch in advance of pull request.
• Standardize on "JIRA" vs "Jira".
• Fix "inclusing" and "commiting" typos.
• Remove extraneous within-paragraph newlines. Add newlines after section headings.

The change to a branch naming convention that would supplement the bare issue identifier in the name with a hint about what the branch is about (UP-4148-contributing vs UP-4148) is dropped because there had been concern that long branch names might be annoying.

[drewwills]

Looks like an improvement 👍

[jameswennmacher]

Looks good. (I like longer branch names too :-) )

[apetro]

@jameswennmacher Yup. Could go after that in a separate Pull Request if desired. Looking to get the uncontroversial improvements adopted through this one.

[timlevett]

👍