FILT: Import Neighbor List filter needs to be written

There is currently no way to import a neighborlist, not even from an existing HDF5 file.

This feature request proposes to create an "Read Neighbor List" filter that reads a neighborlist from a text file. The format of the text file is:
```
# Lines that start with a '#' are comments
[N], [value-0, value-1, ..... value-(N-1)]
```
The Input parameters would be:
FileSystemParameter with "Input File" using normal text file extensions such as .txt, .csv, .dat
Numeric Type parameter so the user can select the proper type for the NeighborList

The output parameters are:

DataArrayCreation parameter. The parent can be anything.

The filter should have some sort of file caching in place so that preflight does not bog down reading the file over and over. There are other filters that implement this scheme.

Start by locating the existing filters that implement file caching, then compare their FileSystemParameter, Numeric Type, and DataArrayCreation usage. Trace how preflight handles file input and how NeighborList types are selected. Done means a Read Neighbor List filter accepts the specified text format, creates the requested data array, and avoids rereading the file during preflight.

Written by the indexing model from the issue text.