ENH: Remove names inputs specialized comparison

With the addition of constant time access to the PrimaryInputs, this
former optimization to make the PrimaryInput the first element in the
map is no longer beneficial. Additionally, with the feature of setting
the name of the primary input, it may not always be beneficial. Also,
for the filters with just one input or output, this offered no
benefit.

Change-Id: I71ee3ce035e3ce9e933153a0ab0f8715c08aec78
PERF: Change default index i/o prefix to just "_"

Renamed default index i/os' prefix from "IndexedDataObject" to just "_"
followed by the index number.

There are two motivation for this: 1) The prior approach required each
comparison done in the named map to compare 17 chars to get to the
number, which is inefficient. 2) With the introduction on the global
variable of these name, shortening the name reduces the ( by a small
amount ) the foot print of the variable.

Change-Id: Ifb9e2fb627f11e001f58090af88b71debb421c98
Merge topic 'NamedInputsCompatibility_NoSpecializedCompare'

1a677ab ENH: Remove names inputs specialized comparison
Merge topic 'GlobalForNamesIndexedInputs'

cea64f0 PERF: Change default index i/o prefix to just "_"