Implement ScriptContext for #2

  * `__FILE__` the script file object
  * `recentWindow` the Firefox's recent window object
Implement ScriptContext - 2 for #2

  * add `getFile` method
  * add `fileToURI` method
  * add `loadScript` method
move getRecentWindow to http_util.jsm for #2
Merge branch 'issue/002-makeScriptContext' into devel