Merge pull request #43 from kazoompa/magma-1.7.x

Magma 1.7.x
Faster getValueSetTimestamps
[artifactory-release] Release version 1.7.5
[artifactory-release] Next development version
Throw parsing exception when an unknown question type is encountered.
OPAL-2075 Merge in opal-1.x
MAGMA-OPAL-2075 - added VARIABLE LABELS type
MAGMA-247 - added condition to prevent creating null-value attributes