File extension sync with titan.core

The following file types are handled by the titan.core and the designer plugin (see the User guide):

• .asn
• .asn1
• .cfg
• .tpd
• .ttcn
• .ttcn3
• .ttcnpp
• .ttcnin

Additional file types handled by the Makefile generation feature:

• .c, .cc, .h, .hh
• .prj
• .3mp