fix(backend): OData/GraphQL pagination should display warning on empty

[ghiscoding]

• add a new paginationOptions getter/setter to avoid incomplete gridOptions passed by the OData result callback, merging the gridOptions was incomplete because it was only merging with the local gridOptions instead of the local+global gridOptions
• basically we won't be able to see the Empty Dataset Warning with OData unless we modified the code and use the new setter. Keeping the old code will still work but just won't display the warning when dataset is empty

[codecov]

Codecov Report

Merging #632 (382c831) into master (8f72e38) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##            master      #632   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files          151       151           
  Lines        10227     10238   +11     
  Branches      3449      3452    +3     
=========================================
+ Hits         10227     10238   +11     

Impacted Files	Coverage Δ
...lickgrid/components/angular-slickgrid.component.ts	100.00% <100.00%> (ø)
...s/angular-slickgrid/services/pagination.service.ts	100.00% <100.00%> (ø)

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[ghiscoding]

this should be replaced with this.gridOptions.pagination = this._paginationOptions;