Fix #74: Harmonize inline spectrum modes 
Fix #74: Harmonize inline spectrum modes 

Introduce input key 'spectrum mode' for inline spectrum definitions,
which has the same meaning as the mode flag in EGSnrc spectrum files.
The input key 'spectrum type' is still recognized, although it is
deprecated from now on.
mchamberland/EGSnrc,ftessier/EGSnrc,ftessier/EGSnrc,marenaud/EGSnrc,MartinMartinov/EGSnrc,marenaud/EGSnrc,ftessier/EGSnrc,MartinMartinov/EGSnrc,crcrewso/EGSnrc,mchamberland/EGSnrc,mchamberland/EGSnrc,crcrewso/EGSnrc,MartinMartinov/EGSnrc,mchamberland/EGSnrc,nrc-cnrc/EGSnrc,nrc-cnrc/EGSnrc,nrc-cnrc/EGSnrc,ftessier/EGSnrc,MartinMartinov/EGSnrc,MartinMartinov/EGSnrc,nrc-cnrc/EGSnrc,mchamberland/EGSnrc,ftessier/EGSnrc,crcrewso/EGSnrc,crcrewso/EGSnrc,marenaud/EGSnrc,nrc-cnrc/EGSnrc,marenaud/EGSnrc,mchamberland/EGSnrc,crcrewso/EGSnrc,ftessier/EGSnrc,marenaud/EGSnrc,marenaud/EGSnrc