added functionality for mixed imaging condition

[MatthewEai]

Updated born accumulation functionality in all 6 reference propagators to allow for the mixed imaging conditon that balances long and short wavelengths. This is controlled by the new parameter RTM_weight

[codecov-commenter]

Codecov Report

❌ Patch coverage is 33.33333% with 72 lines in your changes missing coverage. Please review.
✅ Project coverage is 82.86%. Comparing base (ea1ae2a) to head (a4742ee).
⚠️ Report is 19 commits behind head on master.

Files with missing lines	Patch %	Lines
src/jop_prop2DAcoIsoDenQ_DEO2_FDTD.jl	33.33%	12 Missing ⚠️
src/jop_prop2DAcoTTIDenQ_DEO2_FDTD.jl	33.33%	12 Missing ⚠️
src/jop_prop2DAcoVTIDenQ_DEO2_FDTD.jl	33.33%	12 Missing ⚠️
src/jop_prop3DAcoIsoDenQ_DEO2_FDTD.jl	33.33%	12 Missing ⚠️
src/jop_prop3DAcoTTIDenQ_DEO2_FDTD.jl	33.33%	12 Missing ⚠️
src/jop_prop3DAcoVTIDenQ_DEO2_FDTD.jl	33.33%	12 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master      #52      +/-   ##
==========================================
- Coverage   85.00%   82.86%   -2.14%     
==========================================
  Files          10       10              
  Lines        2320     2416      +96     
==========================================
+ Hits         1972     2002      +30     
- Misses        348      414      +66     

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