feat(editors): change all private keyword to protected for extensability

[ghiscoding]

• also changed all services to readonly

[codecov]

Codecov Report

Merging #680 (5f9148b) into master (7b95401) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##            master      #680   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files          157       157           
  Lines        10458     10458           
  Branches      3515      3515           
=========================================
  Hits         10458     10458           

Impacted Files	Coverage Δ
...es/angular-slickgrid/editors/autoCompleteEditor.ts	100.00% <100.00%> (ø)
...odules/angular-slickgrid/editors/checkboxEditor.ts	100.00% <100.00%> (ø)
...pp/modules/angular-slickgrid/editors/dateEditor.ts	100.00% <100.00%> (ø)
...dules/angular-slickgrid/editors/dualInputEditor.ts	100.00% <100.00%> (ø)
...p/modules/angular-slickgrid/editors/floatEditor.ts	100.00% <100.00%> (ø)
...modules/angular-slickgrid/editors/integerEditor.ts	100.00% <100.00%> (ø)
...odules/angular-slickgrid/editors/longTextEditor.ts	100.00% <100.00%> (ø)
.../modules/angular-slickgrid/editors/sliderEditor.ts	100.00% <100.00%> (ø)
...pp/modules/angular-slickgrid/editors/textEditor.ts	100.00% <100.00%> (ø)

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