Choko command

### How it works:
```
choko start
```
- If the file "./applications/applications.json" exist, will just start the application.
- If not, will create the default directory for applications (in case it not exist already), run the install process, and then start the server in order to continue the install process in the browser.

```
choko start sandbox
```
- If the file "./sandbox/applications.json" exist, will just start the application.
- If not, will create the specified directory for applications (in case it not exist already), run the install process, and then start the server in order to continue the install process in the browser.

So you could start a new application just doing:
```
$ mkdir my-project
$ cd my-project
$ choko start
$ tree
└── applications
    ├── applications.json
    └── localhost
        └── settings.json
```
Since this is a constant, I think we can use [Felix's suggestions](https://github.com/felixge/node-style-guide#use-uppercase-for-constants) on how to name constants.