Merge pull request #82 from heyongjian/master

huangming:merge the main branch to native branch.
fix bug :issue-39, when download a wallpaper, the wallpaper thumbnai applys the preview image.

modify the url of the wallpaper thumbnai image.
Merge pull request #169 from whuthm/master

fix bug :issue-39, when download a wallpaper, the wallpaper thumbnai applys the preview image.