urlencode query_string tag

copy from django.contrib.admin.main.views get_query_string
Initial implementation of sites - created FileBrowserSite class
Implementation of Custom Actions
Site-specific urls
MEDIA_ROOT and DIRECTORY now configurable per-site
Changed MEDIA_ROOT back to a global setting
Resolved following bug: The admin-command fb_version_generate would generate image versions for existing versions (wrong filter patter).
FileBrowseField changed back to original.
Resolved following bug: The admin-command fb_version_generate would generate image versions for existing versions (wrong filter patter).
MEDIA_ROOT made configurable, DIRECTORY completely removed
MEDIA_URL configurable
bug in url_to_path fixed
Field needs a change to work well with per-site media_root and url. Changes in this commit only for testing purposes
Tests adapted.
signals renamed, urls and views completely empty now.
use correct method name in documentation (fixes issue #10)
Fixes and Docs updated (Sites and Custom Actions)
Docs updated
Docs updated.
Comments in now empty files views.py and urls.py