refactor(*): utilize rxjs(5.5 and above) lettable operators

目的：

 - 更清晰地表达一些读入流、输出流的操作，并帮助进一步提取其中的纯函数；
 - 通过 pipe 方法组合纯函数，令流管理更像搭积木；
 - 令每个模块各自对 rxjs 操作符的依赖更清晰。

package.json

@@ -78,7 +78,7 @@
     "npm-run-all": "^4.1.2",
     "nyc": "^11.3.0",
     "raw-loader": "^0.5.1",
-    "rxjs": "^5.5.5",
+    "rxjs": "^5.5.6",
     "shelljs": "^0.8.0",
     "shx": "^0.2.2",
     "sinon": "^4.1.3",

src/operators.ts

@@ -4,19 +4,3 @@ import 'rxjs/add/observable/from'
 import 'rxjs/add/observable/fromPromise'
 import 'rxjs/add/observable/of'
 import 'rxjs/add/observable/throw'
-
-// rxjs Operators
-import 'rxjs/add/operator/catch'
-import 'rxjs/add/operator/combineAll'
-import 'rxjs/add/operator/concatMap'
-import 'rxjs/add/operator/concatMapTo'
-import 'rxjs/add/operator/debounceTime'
-import 'rxjs/add/operator/do'
-import 'rxjs/add/operator/map'
-import 'rxjs/add/operator/mergeMap'
-import 'rxjs/add/operator/publishReplay'
-import 'rxjs/add/operator/skip'
-import 'rxjs/add/operator/skipWhile'
-import 'rxjs/add/operator/switchMap'
-import 'rxjs/add/operator/reduce'
-import 'rxjs/add/operator/take'

src/proxy/index.ts

@@ -1,10 +1,3 @@
-import 'rxjs/add/operator/combineAll'
-import 'rxjs/add/operator/do'
-import 'rxjs/add/operator/map'
-import 'rxjs/add/operator/publishReplay'
-import 'rxjs/add/operator/switchMap'
-import 'rxjs/add/operator/take'
-
 export { QueryToken, SelectorMeta } from '../storage/modules/QueryToken'
 export { ProxySelector } from '../storage/modules/ProxySelector'
 export * from '../interface'