ASN: Rename .asn1 files

When you import ASN.1 modules from the ASN.1 library (from N7S - the PUS library that is built in space creator), the files are not taken into account by the tool

The reason seems to be the file extension: they are .asn1 while space creator expects .asn two options:

1. Rename all the files to .asn
2. Recognise .asn1 as valid ASN.1 files to be parsed