Add basic code for FileLoaderRegistry. Refs #7263

Currently based on string names.
Add DECLARE_FILELOADER_ALGORITHM macro. Refs #7263
Add a simple FileDescriptor class that wraps a file stream

The stream is open for as long as the object is alive.
Refs #7263

FileDescriptor uses streams rather than c file handles. Refs #7263
Allow move_class.py to move untracked files. Refs #7263
Fix AlgorithmFactory::unsubscribe method to updates version map.

It was previously not updating the version map when the algorithm was
removed and then subscribing the same thing again would throw an error.
Refs #7263
Have AlgorithmFactory::subscribe return the class name subscribed.

Refs #7263
Avoid duplicate Algorithm registration in API tests. Refs #7263
FileLoaderRegistry now subscribes algorithms to factory

and also defines two types of loader, NonHDF and HDF.
Refs #7263
Add HDFDescriptor class that will describe HDF files.

The checks for the headers at the start of HDF4 & HDF5 files have been
put in a static isHDF member to encapsulate the details about
checking for a HDF file and make it reusable.
It will not retain an open file handle to the file so does not
inherit from the standard FileDescriptor.
Refs #7263
Add pathExists & classTypeExists checks to HDFDDescriptor. Refs #7263
Implement loader searching in FileLoaderRegistry.

The FileLoaderRegistry can now be asked to search its list of loaders
for the best that matches a given file. It passes along a *Descriptor
object to minimize the number of times the file is opened.

Refs #7263
Add ability to restrict path search in HDF file by type.

Refs #7263
Add root attribute query methods to HDFDescriptor. Refs #7263
Cache first entry name & type in HDFDescriptor. Refs #7263
Refs #7263 Formatting changes only
First lot of updates for new loader check style. Refs #7263
Add static isAscii checks to FileDescriptor class. Refs #7263
General file loader conversion. Refs #7263
Loader search does descriptor callback even if exception thrown.

Refs #7523
Cache isAscii flag in FileDescriptor. Refs #7263