adds plugin level hooks support

1.Support of **js script files only** (nodejs is used to run script file)

2.Support of the following **hook types**

*  beforeinstall/preinstall – run before plugin is installed
*  install/postinstall/afterinstall – run after plugin is installed
*  uninstall – run after plugin is uninstalled

    ```
    <script type="postinstall" src="scripts/postinstall.js" />
    <script type="preinstall" src="scripts/preinstall.js" />
    <script type="install" src="scripts/install.js" />
    ```


3.To retrieve execution parameters **inside hook file**
````
console.log ('\tCORDOVA_PLATFORM: ' + process.env.CORDOVA_PLATFORM);
console.log ('\tCORDOVA_PROJECT_DIR: ' + process.env.CORDOVA_PROJECT_DIR);
console.log ('\tCORDOVA_PLUGIN_DIR: ' + process.env.CORDOVA_PLUGIN_DIR);
console.log ('\tCORDOVA_CMDLINE: ' + process.env.CORDOVA_CMDLINE);
````