Fix a bug where observable properties of a row's entity were being cached

[cwohlman]

Fix a bug where observable properties of a row's entity were being cached, which prevents the row from observing their changes.

http://stackoverflow.com/questions/21858868/make-kogrid-respect-observable-properties

[flyfishMT]

Any reason this hasn't been merged? Thanks

[crissdev]

@flyfishMT Currently there's some effort put to make the library testable. You can see the progress in the 2.1.5 branch. Any help would just speed up things. Thanks.