feat(formatters): add AlignRight and AlignCenter Formatters

[ghiscoding]

• center already existed but we can add alignCenter to be in line with the other alignRight Formatter
• note also that there's no need for alignLeft since everything is aligned to the left in SlickGrid

[codecov]

Codecov Report

Merging #634 (bd653d4) into master (4539cc4) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##            master      #634    +/-   ##
==========================================
  Coverage   100.00%   100.00%            
==========================================
  Files          151       153     +2     
  Lines        10269     10281    +12     
  Branches      3614      3464   -150     
==========================================
+ Hits         10269     10281    +12     

Impacted Files	Coverage Δ
...ngular-slickgrid/formatters/alignRightFormatter.ts	100.00% <100.00%> (ø)
...ules/angular-slickgrid/formatters/boldFormatter.ts	100.00% <100.00%> (ø)
...es/angular-slickgrid/formatters/centerFormatter.ts	100.00% <100.00%> (ø)
.../app/modules/angular-slickgrid/formatters/index.ts	100.00% <100.00%> (ø)

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