Add new PBN capability codes to flightplan remark generator

[ltoenning]

With the new ICAO flightplan format, the PBN capabilities are specified as letter codes, like the equipment codes. They should be listed in the remark field like PBN/A1. Currently, the swift remark generator does not support this new format but can add RNP10 or RNP4 to the remarks only. The remark generator should be adjusted to the new letter codes.

References:

• https://contentzone.eurocontrol.int/fpl/
• https://www.icao.int/EURNAT/Other%20Meetings%20Seminars%20and%20Workshops/PBN%20TF/PBNTF%20-%20EUROCONTROL%20RAISG2/PBNTF-ECTL-RAISG2-PPT04_%20fleet%20equipage%20according%20to%20FPL%20content.pdf