Expand getPlane to allow initialized raw pixels store as an input

When retrieving a large number of planes, initializing a store at each call
is at the detriment of efficiency. This commit allows the user to pass a fully
initialized raw pixels store to getPlane, retrieve the pixels data and keep
the store active.
Fix missing variable assignment
Add both signatures of getPlane to the training example

Add a time elapsed measurement for efficiency comparison
Fix getPlane() using store/pixels object input
Fix the training example to use the new signature
Fix getPlane() doc header
Allow getTile to use pixels and raw pixel store objects
Allow getStack to use pixels and raw pixel store objects
Add new getTile/getStack signature to the training example
Fix narginchk in getTile()
Fix getTile() input parsing
Fix typo
Merge pull request #3028 from sbesson/matlab_getplane_efficiency

Matlab getPlane efficiency