realm-icon: Add realm icon feature.

- Add realm icon fields to realm model.
- Add migration for new realm model's field.
- Add views for icon uploading and deleting.
- Add routes for realm icons views.
- Add JS widget for realm icon upload setting.
- Add realm icon upload to administration
  organization setting.
- Add tests for realm icons.

Fixes #3660.

zerver/views/realm_icon.py

@@ -0,0 +1,55 @@
+from django.shortcuts import redirect
+from django.utils.translation import ugettext as _
+from django.http import HttpResponse, HttpRequest
+
+from zerver.decorator import require_realm_admin
+from zerver.lib.actions import do_change_icon_source
+from zerver.lib.realm_icon import realm_icon_url
+from zerver.lib.response import json_error, json_success
+from zerver.lib.upload import upload_icon_image
+from zerver.models import UserProfile
+
+
+@require_realm_admin
+def upload_icon(request, user_profile):
+    # type: (HttpRequest, UserProfile) -> HttpResponse
+
+    if len(request.FILES) != 1:
+        return json_error(_("You must upload exactly one icon."))
+
+    icon_file = list(request.FILES.values())[0]
+    upload_icon_image(icon_file, user_profile)
+    do_change_icon_source(user_profile.realm, user_profile.realm.ICON_UPLOADED)
+    icon_url = realm_icon_url(user_profile.realm)
+
+    json_result = dict(
+        icon_url=icon_url
+    )
+    return json_success(json_result)
+
+
+@require_realm_admin
+def delete_icon_backend(request, user_profile):
+    # type: (HttpRequest, UserProfile) -> HttpResponse
+    # We don't actually delete the icon because it might still
+    # be needed if the URL was cached and it is rewrited
+    # in any case after next update.
+    do_change_icon_source(user_profile.realm, user_profile.realm.ICON_FROM_GRAVATAR)
+    gravatar_url = realm_icon_url(user_profile.realm)
+    json_result = dict(
+        icon_url=gravatar_url
+    )
+    return json_success(json_result)
+
+
+def get_icon_backend(request, user_profile):
+    # type: (HttpRequest, UserProfile) -> HttpResponse
+    url = realm_icon_url(user_profile.realm)
+
+    # We can rely on the url already having query parameters. Because
+    # our templates depend on being able to use the ampersand to
+    # add query parameters to our url, get_icon_url does '?version=version_number'
+    # hacks to prevent us from having to jump through decode/encode hoops.
+    assert '?' in url
+    url += '&' + request.META['QUERY_STRING']
+    return redirect(url)