adding BOM to csv export

[lgelauff]

Should resolve #130 . Haven't been able to test locally though, so please tread with caution. Reusing from example here

[codecov-commenter]

Codecov Report

Merging #194 (d756b18) into master (fe5dc80) will decrease coverage by 0.02%. The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #194      +/-   ##
==========================================
- Coverage   76.49%   76.46%   -0.03%     
==========================================
  Files          19       19              
  Lines        3820     3820              
  Branches      479      479              
==========================================
- Hits         2922     2921       -1     
  Misses        655      655              
- Partials      243      244       +1     

Impacted Files	Coverage Δ
montage/admin_endpoints.py	82.32% <100.00%> (ø)
montage/rdb.py	77.83% <0.00%> (-0.06%)	:arrow_down:

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