Bump most dependencies to recent versions

This patch bumps most dependencies to recent versions, which should
resolve many Dependabot alerts. In addition to that, it allows all the
tests to finally run successfully.

Author: ldionne

requirements.client.txt

@@ -2,16 +2,16 @@
 # The client has fewer requirements than the server code.
 .
 aniso8601==1.2.0
-click==6.7
-Flask-RESTful==0.3.4
-Flask-WTF==0.12
-Flask==0.12.2
-itsdangerous==0.24
-Jinja2==2.11.3
-MarkupSafe==1.1.1
+click==8.1.8
+Flask-RESTful==0.3.10
+Flask-WTF==1.2.0
+Flask==3.1.2
+itsdangerous==2.2.0
+Jinja2==3.1.6
+MarkupSafe==3.0.3
 python-gnupg==0.3.7
 pytz==2016.10
 SQLAlchemy==1.3.24
-Werkzeug==0.15.6
-WTForms==2.0.2
-pyyaml==5.1.2
+Werkzeug==3.1.3
+WTForms==3.2.1
+pyyaml==6.0.3