Revert "Fix version numbers to be 5.0.0-rc1 instead of 5.0.0-RC1"

This reverts commit 4d37652886ba5e0f45977598e5f66b75e218db1b.
Revert "Switch 5.0.0-beta2 version numbers to 5.0.0-RC1"

This reverts commit 508b8346e0747635e3a7614c3de640e3606d9621.
Revert "Update POM version numbers to 5.0.0-beta2"

This reverts commit 2ade8fd70a4927adfbdf5ca884a312b12894a37f.
Fix version numbers to be 5.1.0-SNAPSHOT instead of 5.0.0-SNAPSHOT

The develop branch is 5.1.0-SNAPSHOT; the dev_5_0 branch is 5.0.0-SNAPSHOT.
Merge pull request #835 from melissalinkert/revert-version-number

Set POM versions to 5.1.0-SNAPSHOT