[ngx-table] Detail & context rows: abstract similar logic

[WHeirstrate]

In general, I think both this context & detail feature have too much overlap. Consider splitting the way you render your row to a separate component and allowing implementations to overwrite / extend the specifics.

This obviously exceeds the scope of this change and warrants a breaking change but does provide more flexiblit. From what I understand, at the time of writing, the only difference between context & detail is top & bottom respectively.

Originally posted by @ian-emsens-shd in #446 (review)