fix(header): re-create header grouping title after changing picker cols

[ghiscoding]

• after hiding/showing columns from ColumnPicker/GridMenu we need to re-create the header grouping titles

[codecov]

Codecov Report

Merging #502 into master will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##            master      #502    +/-   ##
==========================================
  Coverage   100.00%   100.00%            
==========================================
  Files          148       148            
  Lines         9556      9564     +8     
  Branches      3192      3330   +138     
==========================================
+ Hits          9556      9564     +8     

Impacted Files	Coverage Δ
...r-slickgrid/services/groupingAndColspan.service.ts	100.00% <100.00%> (ø)

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