nicer error message on mastodon app creation failure

also log more exceptions to sentry

routes.py

@@ -88,6 +88,8 @@ def twitter_login_step1():
             **app.config.get_namespace("TWITTER_")
             ))
     except (TwitterError, URLError):
+        if sentry:
+            sentry.captureException()
         return redirect(
                 url_for('index', twitter_login_error='', _anchor='log_in'))
 
@@ -112,6 +114,8 @@ def twitter_login_step2():
         set_session_cookie(session, resp, app.config.get('HTTPS'))
         return resp
     except (TwitterError, URLError):
+        if sentry:
+            sentry.captureException()
         return redirect(
                 url_for('index', twitter_login_error='', _anchor='log_in'))
 
@@ -144,6 +148,8 @@ def upload_tweet_archive():
 
         return redirect(url_for('index', _anchor='recent_archives'))
     except (BadZipFile, TweetArchiveEmptyException):
+        if sentry:
+            sentry.captureException()
         return redirect(
                 url_for('index', tweet_archive_failed='',
                         _anchor='tweet_archive_import'))
@@ -160,6 +166,8 @@ def settings():
                 setattr(viewer, attr, request.form[attr])
         db.session.commit()
     except ValueError:
+        if sentry:
+            sentry.captureException()
         return 400
 
     return redirect(url_for('index', settings_saved=''))
@@ -267,17 +275,17 @@ def api_viewer_timers():
 
 @app.route('/login/mastodon', methods=('GET', 'POST'))
 def mastodon_login_step1(instance=None):
+
+    instance_url = (request.args.get('instance_url', None)
+                    or request.form.get('instance_url', None))
+
+    if not instance_url:
         instances = (
             MastodonInstance
             .query.filter(MastodonInstance.popularity > 1)
             .order_by(db.desc(MastodonInstance.popularity),
                       MastodonInstance.instance)
             .limit(30))
-
-    instance_url = (request.args.get('instance_url', None)
-                    or request.form.get('instance_url', None))
-
-    if not instance_url:
         return render_template(
                 'mastodon_login.html', instances=instances,
                 address_error=request.method == 'POST',
@@ -289,6 +297,7 @@ def mastodon_login_step1(instance=None):
     callback = url_for('mastodon_login_step2',
                        instance=instance_url, _external=True)
 
+    try:
         app = lib.mastodon.get_or_create_app(
                 instance_url,
                 callback,
@@ -299,6 +308,11 @@ def mastodon_login_step1(instance=None):
 
         return redirect(lib.mastodon.login_url(app, callback))
 
+    except Exception:
+        if sentry:
+            sentry.captureException()
+        return redirect(url_for('mastodon_login_step1', error=True))
+
 
 @app.route('/login/mastodon/callback/<instance>')
 def mastodon_login_step2(instance_url):