Refactored URLs of tail client

Signed-off-by: Stephan Hagemann <stephan@pivotallabs.com>
Made space_id optional in logMessage protobuffer

Signed-off-by: Stephan Hagemann <stephan@pivotallabs.com>
Make organization_id required in the logMessage protobuffer

Signed-off-by: Stephan Hagemann <stephan@pivotallabs.com>