Eliminate duplicate namespace prefixes: fedora and fcrepo

Resolves: https://www.pivotaltracker.com/story/show/83422816
[maven-release-plugin] prepare release fcrepo-4.0.0
[maven-release-plugin] prepare for next development iteration
Prevent versions from being created when provided label conflicts.
Merge pull request #670 from mikedurbin/version-label-conflict-bug

Prevent versions from being created when provided label conflicts.

Resolves: https://jira.duraspace.org/browse/FCREPO-1242
Avoided a server error when returning a version location with a space.
Merge pull request #671 from mikedurbin/version-label-with-spaces

Avoided a server error when returning a version location with a space.
Upgrade ModeShape to version 4.1.0.Final
- Remove manual observation unregistration

Resolves: https://jira.duraspace.org/browse/FCREPO-1249