Compare cellphonedb and version 3 compatibility

[zktuong]

• Add new function to compare cellphonedb results across conditions
• Add new function to plot compare cellphonedb results across conditions
• cellphonedb version 3 compatibility

[codecov]

Codecov Report

Merging #33 (3ec991f) into master (85ecc9e) will increase coverage by 4.92%.
The diff coverage is 83.25%.

@@            Coverage Diff             @@
##           master      #33      +/-   ##
==========================================
+ Coverage   67.41%   72.34%   +4.92%     
==========================================
  Files          10       11       +1     
  Lines        1338     1750     +412     
==========================================
+ Hits          902     1266     +364     
- Misses        436      484      +48     

Impacted Files	Coverage Δ
R/plot_cpdb.R	75.69% <50.00%> (+4.65%)	⬆️
R/compare_cpdb.R	83.37% <83.37%> (ø)
R/plot_cpdb2.R	79.72% <100.00%> (ø)

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