PERF: Use iterators into name map for index inputs

This patch add an additional std::vector to the ProcessObject which
contains iterators into the names inputs map. This removes the need to
allocate a string, and perform a map look up, and replaces it with
constant time access to the DataObject inputs.

Change-Id: I0d62f874ea58a57bc3fe1c7639cd2c7e5195df88
ENH: index can be associated with required input

Current ITK filters have indexed input without names. To migrate these
classes to have named inputs, names need to be associated with the
current index to maintains compatibility.

The addition of an optional argument to ProcessObject's
AddRquiredInputName method is used to connect the two different
indexing types for the filter's input.

The SetPrimaryInputName method was re-factored to only call existing
methods and not directly manipulate the internal structures.

Change-Id: Iaa20c88eff270f95ada0ea52fba69ebf366a5f45
PERF: Add global variable of index names in ProcessObject

Many calls to ProcessObject's Inputs/Outputs methods need to construct
a string with the named index. This patch converts from the procedural
approach to used a constant global variable for the first 100 names
indexed inputs.

Change-Id: I0daa7afe431b1254e07ae1e0542325b5bd33699d
Merge topic 'NamedInputsCompatibility'

b6ff674 ENH: index can be associated with required input
488d9ed PERF: Use iterators into name map for index inputs
Merge topic 'GlobalForNamesIndexedInputs'

8bcd6e9 PERF: Add global variable of index names in ProcessObject