v0.5.0

This release stops a missing icon from breaking a page: a block variant that
names an icon removed in an earlier release now renders without it and logs
a warning, instead of answering with a server error.

Upgrading from 0.4.0 — read this first:

• dashboard_icon_path is gone (see Removed). Templates of your own that
  use it, or pass icon to phoxtail_core/copy_key_button.html, must switch
  to {% icon %}.

Removed

• The dashboard_icon_path template tag is removed, and so is the icon
  parameter of phoxtail_core/copy_key_button.html. Every icon is now drawn
  with {% icon "<name>" %}, so a missing name renders nothing and logs a
  warning everywhere instead of failing the page in the dashboard navigation.
  Templates that used {% dashboard_icon_path name as path %}{% include path %}
  should use {% icon name %}.

Fixed

• A page whose block variant names an icon that no longer exists now renders
  without that icon instead of failing with a server error. The {% icon %}
  tag logs a warning naming the missing icon (Icon '<name>' not found), so
  stored variants that still use a name removed in an earlier release can be
  found and fixed.