Replace geotiffread with readgeoraster throughout the repo

[wschwanghart]

geotiffread has been replaced by readgeoraster. Reading geotiffs is central to the constructor function GRIDobj and several I/O functions including readopentopo. The replacement requires different handling of projections. These will be addressed in another issue.
I label this issue as a bug because readopentopo has problems with reading certain DEMs which geotiffread is unable to read, but readgeoraster can read. Fixing this issue maintains a dependency of TopoToolbox on the Mapping Toolbox.