[Tizen] New discovery page for devtools

Add basic decorates to discovery page of devtools to improve user experience.
The followings are the current and imporved discovery page.

![old-devtools](https://cloud.githubusercontent.com/assets/3304318/4230005/7e291412-397c-11e4-8fba-adc966b41964.png)
![new-devtools](https://cloud.githubusercontent.com/assets/3304318/4230006/8232a708-397c-11e4-935c-53593cd271ba.png)


BUG=https://crosswalk-project.org/jira/browse/XWALK-2525
can we somehow load icon from the resources in filesystem?