add more error checking to -*-import-label, make GiftiLabel maintain an invariant of keeping the colors valid

Hid rotation controls on the Clipping Planes Dialog.  Currently the controls are disabled and leaving the controls disabled but visible may confuse users.

New clipping planes are working (with the exception of rotation), next step is to remove old clipping plane code.

Finished redesign of nodes inside border algorithm and it is working on all of Matt's border where it was previously failing.

Improve but not completely fix nodes inside border.  The remaining problem is that some borders are very skinny and as the borders are moved to the nearest vertices, point in the opposite side of a border become immediate neighbors and end up closing a small region of the border.

fix bug in -cifti-cross-correlation due to misuse of loop index when using counter to do in-order row loading within parfor
remove unused variables from -volume-gradient

Algorithm was failing for a clockwise border on the medial side of a right hemisphere.  If the number of nodes is still greater than half the surface number of nodes then the algorithm has failed.  In this case, invert the selection and remove the nodes in the connected path from the nodes inside the border.

another improvement to -cifti-convert documentation, to reduce the temptation to try to use it instead of -cifti-create-*

provisional new short description for -cifti-convert to steer people away from using it for -cifti-create-*
make XnatTest fail early with informative message

improve -cifti-convert help to mention -cifti-create commands, remove obsolete warning about overwriting