Compatibility fixes.

[alxp]

What does this Pull Request do?

Compatibility fixes and improvements that we have been running as a fork.

What's new?

1. Update README to change Islandora 8 to Islandora 2
2. Migrate Plus version dependency update
3. Fix broken authentication in islandora_files migration.
4. Improved islandora_objects migration:
5. Add 'isMemberOf' along with 'isMemberOfCollection' to the field_member_of destination.
6. Don't bail on an object if it's a member of a collection that is not in the current migration.

• Does this change require documentation to be updated? No

• Does this change add any new dependencies?
  Migrate Conditions

• Does this change require any other modifications to be made to the repository No

• Could this change impact execution of existing code? No

How should this be tested?

Have access to an Islandora 7 site with standard objects such as books and pages.

Follow the instructions in the README to migrate sample content to a new or existing Islandora 2 site.

Additional Notes:

We are embarking on a books migration so further updates will come as we encounter issues.

Interested parties

Tag (@ mention) interested parties or, if unsure, @Islandora-Devops/committers

[alxp]

Created a 2.x base branch to account for dependency update and bring in line with Islandora.