Maintenance Release

• add /listlabels to labelmap
• do fsync on logs to guarantee writes in exchange of throughput
• add public versions and Google id auth
• add ability to set next labels in labelmap
• add more efficient /indices-compressed to labelmap
• force directory creation for json mutation log
• don't let server start if mutations jsonstore can't be created when specified
• By default, release distribution tarball uses dvid-web-console 2.1.7
• allow repo-level rename/new instance rpc on locked node

Note: No Mac tarball yet.