fix creating dbc files.

[ebroecker]

• arbitration_id instead of combound arbitration id was used in several cases
• ecu attribute definitions were not written, inspite signal attribute definitions were
  written

[codecov-io]

Codecov Report

Merging #337 into development will not change coverage.
The diff coverage is 50%.

@@             Coverage Diff              @@
##           development     #337   +/-   ##
============================================
  Coverage        40.18%   40.18%           
============================================
  Files               35       35           
  Lines             7053     7053           
  Branches          1669     1669           
============================================
  Hits              2834     2834           
  Misses            4010     4010           
  Partials           209      209

Impacted Files	Coverage Δ
src/canmatrix/formats/dbc.py	52.4% <50%> (ø)	⬆️

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