Add cc.moduleLoader to load js by moduleConfig.json.

Abandon `jsList` in `project.json`, instead, use `userModules`.

For example:

```
+framework
    +userModule1
        -moduleConfig.json
+lib
    +userModule2
        -moduleConfig.json
+src
    -moduleConfig.json

-project.json
```

`framework/userModule1/moduleConfig.json` and  `lib/userModule2/moduleConfig.json` and `src/moduleConfig.json`: 

```
{
    module : {
        "sub1" : ["a.js", "b.js"],
        "sub2":["c.js","d.js"],
        "default":["sub1","sub2"]
    }
}
```

`project.json`:

```
"userModules" : [
    {"framework/userModule1":["sub1"]},
    {"lib/userModule1":["default"]},
    "src"
]
```