url preview: Enable server level setting for url embed previews.

This significantly simplifies the process for enabling this feature in
new organizations.

docs/overview/changelog.md

@@ -7,6 +7,19 @@ All notable changes to the Zulip server are documented in this file.
 This section lists notable unreleased changes; it is generally updated
 in bursts.
 
+**Upgrade notes:**
+
+- The defaults for Zulip's inline URL preview setting have changed.
+Previously, the server-level `INLINE_URL_EMBED_PREVIEW` setting was
+disabled, and organization-level setting was enabled.  Now, the
+server-level setting is enabled by default, and the organization-level
+setting is disabled.  As a result, organization administrators can
+configure this feature entirely in the UI.  However, servers that had
+previously [enabled previews of linked
+websites](https://zulipchat.com/help/allow-image-link-previews) will
+lose the setting and need to re-enable it.
+
+
 ### 2.0.3 -- 2019-04-23
 
 - Added documentation for upgrading the underlying OS version.

docs/production/settings.md

@@ -101,8 +101,6 @@ Some popular settings in `/etc/zulip/settings.py` include:
 * The Twitter integration, which provides pretty inline previews of
   tweets.
 * The email gateway, which lets users send emails into Zulip.
-* `INLINE_URL_EMBED_PREVIEW`, which controls our experimental feature
-  providing inline previews of links pasted into Zulip.
 
 ## Zulip announcement list
 

zproject/dev_settings.py

@@ -1,4 +1,3 @@
-
 # For the Dev VM environment, we use the same settings as the
 # sample prod_settings.py file, with a few exceptions.
 from .prod_settings_template import *
@@ -73,9 +72,6 @@ USING_PGROONGA = True
 # Flush cache after migration.
 POST_MIGRATION_CACHE_FLUSHING = True  # type: bool
 
-# Enable inline open graph preview in development for now
-INLINE_URL_EMBED_PREVIEW = True
-
 # Don't require anything about password strength in development
 PASSWORD_MIN_LENGTH = 0
 PASSWORD_MIN_GUESSES = 0

zproject/prod_settings_template.py

@@ -274,7 +274,7 @@ FEEDBACK_EMAIL = ZULIP_ADMINISTRATOR
 # Controls whether or not Zulip will provide inline previews of
 # websites that are referenced in links in messages.  Note: this feature
 # can also be disabled in a realm's organization settings.
-#INLINE_URL_EMBED_PREVIEW = False
+#INLINE_URL_EMBED_PREVIEW = True
 
 # Controls whether or not Zulip will parse links starting with
 # "file:///" as a hyperlink (useful if you have e.g. an NFS share).

zproject/settings.py

@@ -223,7 +223,7 @@ DEFAULT_SETTINGS = {
     'ENABLE_FILE_LINKS': False,
     'ENABLE_GRAVATAR': True,
     'INLINE_IMAGE_PREVIEW': True,
-    'INLINE_URL_EMBED_PREVIEW': False,
+    'INLINE_URL_EMBED_PREVIEW': True,
     'NAME_CHANGES_DISABLED': False,
     'AVATAR_CHANGES_DISABLED': False,
     'PASSWORD_MIN_LENGTH': 6,