Servo Block. Permit different servo types

Servo 'attach' with matching specifications to achieve 180 degree rotation.

More gracefully insist that 'pin number' must be a constant.

Includes new 'number-const' GenusType that uses 'number-list' connector.
FIX. Logical Test block do not clone correctly.
Merge remote-tracking branch 'upstream/master'
Merge remote-tracking branch 'origin/master' into FIX_LogicalTestCloneWrongly
Tiny typo correction
Merge pull request #63 from TonyCallear/FIX_LogicalTestCloneWrongly

Fix logical test blocks do not clone properly. See issue #36