sigrok-fwextract-kingst-la2016: rephrase resource file writer

Rearrange the res_writer class of the KingstVis firmware extractor.

Separate the bytes/hexfile handling from file writing. Get the CRC
in that data handing part. Which leaves data processing to internal
helpers, while the calling public routine has all details available,
to provide a more helpful log message to users.

Separate the resource enumeration from the output file creation. Which
prettifies the output (sorted order), and allows future implementations
to easier filter the output if desired.