Decoder update: improve speed

Sample file obtained from @nurnberg containing a total of 27641 frames.

Numbers below are produced on the same machine, running on the same data file.

Old version (master):

[13:14:02.115]    QUIET: Reading Clicpix2 rawdata from: /tmp/run25216.csv
[13:15:39.446]    QUIET: ...all written.

total time: 37sec

New version (this branch):

 ../bin/clicpix2_rawdecoder -d /tmp/run25216.csv -m ../config/matrix.cfg -v QUIET
[13:10:22.477]    QUIET: Reading Clicpix2 rawdata from: /tmp/run25216.csv
[13:10:53.366]    QUIET: ...all written.

total time: 31sec

Looks like we won't get any faster without major refactoring. Probably not worth the effort.