Removed _indices, which became a duplicate of _get_indices once it as made private last week
Fixes in Core._interleave_data
- It no longer scans for nans to check if interleave processes was successful, so might be faster
- It didn't work properly on Phases if a non-existing property was called, not sure why but is now fixed
Some playing around with a GenericMixture object.  Not sure if this will work yet.