Packet.GetDataType does not support complex data types

[CBielstein]

Description

While many APRS packet types are determined by their first character alone, some are more complex and can have ! or _ further in to the packet to change the type. Currently, the code responsible for detecting this (Packet.GetDataType) does not take these advanced considerations in to account and only uses the first character.

This should be corrected based on the APRS spec.

Acceptance Criteria

• Handles weather type packets (which can have _ somewhere further in the packet to indicate weather)
• Any reference to this issue are resolved in the code, either by remove test skips or handling caveats called out in comments
• Tests added for other cases from APRS spec