ENH: Turn off DCMTK Logger messages by default

Reading DICOM Image files will sometimes generate thousands of
DCMTK warnings, even though all the DICOM tags needed to extract
Image data and metadata are read correctly.

This patch turns off the DCMTK logger except for fatal errors.
New Set/GetLogLevel are added to control DCMTK logging. A user
might well want to turn on more verbose output from DCMTK while
debugging.

Change-Id: I152aa446b7620b8268f74436e968c21e54b59101
STYLE: dynamic_cast to pointer does not throw

Not need for try catch block when operator can't throw. dynamic_cast
may throw for conversion to a reference type, not a pointer.

Change-Id: Ifa9baa9a30a9a0b23b2e9bfc84481c89831a016c
COMP: Fix "unused-local-typedefs" warnings

These were easy removals of unused typedefs.

Change-Id: I1cc1f3abae12b007e56eaa163da846bf9b8f5037
Merge topic 'fix-unused-typedef-warnings'

ee63f94b COMP: Fix "unused-local-typedefs" warnings
Merge topic 'DynamicCastDoesNotThrow'

627c2f14 STYLE: dynamic_cast to pointer does not throw
Merge topic 'SILENCE_DCMTK_WARNINGS'

934940b8 ENH: Turn off DCMTK Logger messages by default