[Tizen] Enable background-support attribute in settings element.

When "background-support" is enabled in config.xml application will not suspend when goes background.
* enable: Web Application's execution MUST NOT be suspended when it is put into background
* disable: Web Application's execution MUST be suspended when it is put into
  background

BUG=XWALK-1148
TizenSettingInfo only will be created in Setting handler, and make sure to initialize it in parser. If you do not like this, I can re-factor all of these in another PR.