[org] Add org member quota option
[ajax] Remove repo checking when deleting a repo
[thumbnail] Show image file's thumbnail

Conflicts:
	seahub/views/ajax.py
	seahub/views/repo.py
[preview] Show image file's preview

Conflicts:
	seahub/views/repo.py
[repo] image thumbnail & preview: bug fix & improvements
Merge branch '4.0'
[web-api] Return dst-repo-id when move a file
Clean unused files
Merge pull request #312 from haiwen/4.0-web-api-fix

[web-api] Return dst-repo-id when move a file
Remove dirent sorting, and fix some code style