feat(services): make everything extendable by using protected

[ghiscoding]

• it was mentioned by a user of Angular-Slickgrid that it would be nice to extend some of the Services and so I decided to make them all extendable by using protected instead of private

[codecov]

Codecov Report

Merging #411 (a4588ea) into master (502cc0e) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##            master      #411   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files          219       219           
  Lines        13329     13329           
  Branches      4555      4555           
=========================================
  Hits         13329     13329           

Impacted Files	Coverage Δ
packages/common/src/services/gridEvent.service.ts	100.00% <ø> (ø)
packages/binding/src/binding.service.ts	100.00% <100.00%> (ø)
packages/common/src/filters/filterFactory.ts	100.00% <100.00%> (ø)
...ages/common/src/services/backendUtility.service.ts	100.00% <100.00%> (ø)
...ckages/common/src/services/bindingEvent.service.ts	100.00% <100.00%> (ø)
packages/common/src/services/collection.service.ts	100.00% <100.00%> (ø)
packages/common/src/services/extension.service.ts	100.00% <100.00%> (ø)
packages/common/src/services/grid.service.ts	100.00% <100.00%> (ø)
packages/common/src/services/gridState.service.ts	100.00% <100.00%> (ø)
.../common/src/services/groupingAndColspan.service.ts	100.00% <100.00%> (ø)
... and 15 more

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