Allow master-detail style visualization with igxGrid

[ChronosSF]

Is your feature request related to a problem? Please describe.

I want to be able to create a master-detail view with igxGrid, where the master is the grid rows that are expandable and expanding them shows custom template / component for their details.

Describe the solution you'd like

Clear-cut way for defining "details" template for grid rows.

Describe alternatives you've considered

N/A

Additional context

N/A

[MayaKirova]

@StefanIvanov @radomirchev @rkaraivanov @ChronosSF @kdinev

As previously discussed this will be a feature of the igxGrid ( will not affect the other grids - TreeGrid and HierarchicalGrid).
In order to differentiate from the GroupBy feature, which also renders expander indicators, when master-detail template is defined it will render expander inside the cell and will no have an expand/collapse indicator in the header (like in the TreeGrid) :

[MayaKirova]

@radomirchev @kdinev @rkaraivanov @ChronosSF

Please review the initial spec and let me know what you think:
https://github.com/IgniteUI/igniteui-angular/wiki/Grid-Master-Detail

[kdinev]

@MayaKirova I have made some changes and have signed it off on my end.