Convert Admin views to use forms with validation

[miketheman]

Sometimes when interacting with the Admin UI, data validation in forms is not as robust as it could be, leading to the occasional exception raised.

There are currently 100 views configured in Admin-related views, and 26 of them use POST methods:

$ ag "@view_config" "warehouse/admin/views/" --py --filename --count
warehouse/admin/views/helpscout.py:1
warehouse/admin/views/observations.py:1
warehouse/admin/views/ip_addresses.py:2
warehouse/admin/views/prohibited_user_names.py:2
warehouse/admin/views/flags.py:2
warehouse/admin/views/core.py:1
warehouse/admin/views/emails.py:3
warehouse/admin/views/includes.py:2
warehouse/admin/views/sponsors.py:6
warehouse/admin/views/banners.py:7
warehouse/admin/views/prohibited_email_domains.py:3
warehouse/admin/views/journals.py:1
warehouse/admin/views/macaroons.py:4
warehouse/admin/views/organizations.py:13
warehouse/admin/views/malware_reports.py:10
warehouse/admin/views/users.py:16
warehouse/admin/views/prohibited_project_names.py:6
warehouse/admin/views/quarantine.py:1
warehouse/admin/views/projects.py:19

$ ag "request_method=\"POST" warehouse/admin/views | wc -l
      26

Not all views need forms, but those that perform some sort of inline validation, should be using forms.

There are two tasks here (so far):

1. Audit the admin views that use POST, determine how much inline validation they perform today, and add a subtask here with links
2. Resolve each subtask as necessary

Finally, close out this issue when all subtasks are resolved.