test(windowCount): add comprehensive marble tests
test(windowCount): add comprehensive marble tests

Add tests for windowCount that mirror RxJS legacy's tests, and cover
corner cases like Never and Empty. The tests assume the first window is
opened immediately, just like windowTime and window do, and so does
legacy's windowWithCount.

Igorbek/rxjs5,jayphelps/rxjs,RxJS-CN/RxJS-Docs-CN,ReactiveX/rxjs,ReactiveX/RxJS,elliotschi/rxjs,martinsik/rxjs,kwonoj/RxJS,jinroh/RxJS,jadbox/RxJS,ReactiveX/rxjs,jinroh/RxJS,kwonoj/RxJS,SangKa/RxJS-Docs-CN,justinwoo/RxJS,mattpodwysocki/RxJS,robwormald/RxJS,elliotschi/rxjs,figueredo/RxJS,RxJS-CN/RxJS-Docs-CN,jayphelps/rxjs,jayphelps/rxjs,figueredo/RxJS,SangKa/RxJS-Docs-CN,jadbox/RxJS,Igorbek/rxjs5,IgorMinar/RxJS,Brocco/RxJS,Igorbek/rxjs5,jayphelps/rxjs,Brocco/RxJS,justinwoo/RxJS,gluck/RxJS,ReactiveX/RxJS,ReactiveX/rxjs,adrianomelo/RxJS-1,justinwoo/RxJS,elliotschi/rxjs,trxcllnt/RxJS,mattpodwysocki/RxJS,figueredo/RxJS,ReactiveX/RxJS,kwonoj/RxJS,robwormald/RxJS,mattpodwysocki/RxJS,ReactiveX/RxJS,benlesh/RxJS,IgorMinar/RxJS,staltz/RxJSNext,gluck/RxJS,jadbox/RxJS,SangKa/RxJS-Docs-CN,justinwoo/RxJS,robwormald/RxJS,gluck/RxJS,jadbox/RxJS,RxJS-CN/RxJS-Docs-CN,jinroh/RxJS,ReactiveX/rxjs,adrianomelo/RxJS-1,staltz/RxJSNext,saneyuki/RxJS,staltz/RxJSNext,benlesh/RxJS,adrianomelo/RxJS-1,adrianomelo/RxJSNext,SangKa/RxJS-Docs-CN,elliotschi/rxjs,figueredo/RxJS,benlesh/RxJS,Brocco/RxJS,martinsik/rxjs,Brocco/RxJS,staltz/RxJSNext,Igorbek/rxjs5,gluck/RxJS,robwormald/RxJS,adrianomelo/RxJSNext,adrianomelo/RxJSNext,jayphelps/rxjs,martinsik/rxjs,trxcllnt/RxJS,martinsik/rxjs,RxJS-CN/RxJS-Docs-CN,trxcllnt/RxJS,benlesh/RxJS,saneyuki/RxJS,trxcllnt/RxJS,kwonoj/RxJS,adrianomelo/RxJSNext,jinroh/RxJS,mattpodwysocki/RxJS,adrianomelo/RxJS-1