Discrepancy between EGSnrc ctcreate and egs_glib egsphant media encoding

[ftessier]

This issue was reported in https://github.com/clrp-code/egs_brachy/issues/22.

Briefly, #633 expanded the number of media in the EGSnrc ctcreate to 95. However, the number of media was also independently expanded in egs_glib in the development of egs_brachy, but using a different encoding. As a result, egsphant files are being created using inconsistent encodings, leading to undefined behaviour and egs_view crashes.

The proposed solution is to change the ctcreate encoding to match the one in egs_glib (estimated to be used more widely), and perhaps add support for an encoding string inside the egsphant file, for flexibility and perfect clarity.