Bumped pom-scijava to 1.67

Updates SCIFIO to 0.5.1, which includes critical bug fixes over the
0.5.0 release.
DefaultDatasetService: remove ImgOpener hack

ImgOpener no longer has generic method signatures that do not accept a
typed parameter. These were making compilation by javac impossible,
necessitating this ImgOpener hack.

Every method that doesn't take a type parameter in ImgOpener is now
rawtyped, allowing compatibility with javac again.
DefaultDatasetService: fix ImgSaver context

Instead of calling setContext after construction (which throws an
exception, as the context is already set) directly pass the context at
construction.
DefaultDatasetService: default to PLANAR img types

Try to open images as PlanarImgs first, as currenty these are the only
types that support saving.

SCIFIOCellImg will still be used if the image does not fit in memory.