adds viewForHeaderInSection delegate method

[taberrr]

[codecov-io]

Codecov Report

Merging #63 into master will decrease coverage by 1.19%. The diff coverage is 54.54%.

@@            Coverage Diff            @@
##           master      #63     +/-   ##
=========================================
- Coverage    96.5%   95.31%   -1.2%     
=========================================
  Files           3        3             
  Lines         315      320      +5     
=========================================
+ Hits          304      305      +1     
- Misses         11       15      +4

Impacted Files	Coverage Δ
...roller/CollapsibleTableSectionViewController.swift	91.25% <25%> (-3.56%)	:arrow_down:
...ionViewController/CollapsibleTableViewHeader.swift	86.66% <71.42%> (-1.27%)	:arrow_down:

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[taberrr]

@jeantimex could you pls disable whatever this Codecov stuff is? Thx!