This would allow folder image get the path bar's allocated height dynamicly, and make sure it is just aligned with location bar.

if not, location buttons box will 'shrink' when go to a fully english path.
request a height for folder_image same as path entry can solve this problem.

the existing preview implementations can cause crashes when previewed in a list view.

1.drag from other widget to sidebar can resopnse;
2.forbid adding non-directory file to sidebar.

Add a image search interface, when right click a image type file in content view, "Image Search" will be shown.
This selection option will go to a search directory, and can provide an interface to show any files set in localhost.

右键点击图片类型的文件，菜单中会有额外的"Image Search"选项，点击之后会进入新的文件管理器页面，用于展示搜索的结果（可以控制是不是新建窗口，目前是）；
搜索结果展示的是右键选取的图片，因为目前还没有实现后台的服务，想要展示更多的文件，需要将这些文件加入到SearchThreadData的uri_hits这个GList中去。