Rework user profile settings

Accessibility:

- improved semantic layout
- Fixes unlabelled input for custom pronouns. CC @hazy
- Adds labels to dropdowns.
- Shortens certain texts for less verbose screen reader outputs and
  people with slow reading speed.
- Turned optional username rename helper text with low contrast into
  "normal" help text.

UI/UX:

- Removes section about primary email which is no longer managed in the
  profile section.
- Fixes section about primary email not displaying in user settings when notifications are
  not available.
- Removes primary email display, because it is not actually a form
  element here. (Alternatively, we could display it and link to the
account settings for managing the email)

options/locale/locale_en-US.ini

@@ -748,13 +748,14 @@ blocked_users = Blocked users
 public_profile = Public profile
 biography_placeholder = Tell others a little bit about yourself! (Markdown is supported)
 location_placeholder = Share your approximate location with others
-profile_desc = Control how your profile is shown to other users. Your primary email address will be used for notifications, password recovery and web-based Git operations.
+profile_desc = About you
 password_username_disabled = Non-local users are not allowed to change their username. Please contact your site administrator for more details.
 full_name = Full name
 website = Website
 location = Location
 pronouns = Pronouns
 pronouns_custom = Custom
+pronouns_custom_label = Custom pronouns
 pronouns_unspecified = Unspecified
 update_theme = Change theme
 update_profile = Update profile
@@ -849,7 +850,7 @@ add_email_success = The new email address has been added.
 email_preference_set_success = Email preference has been set successfully.
 add_openid_success = The new OpenID address has been added.
 keep_email_private = Hide email address
-keep_email_private_popup = This will hide your email address from your profile. It will no longer be the default for commits made via the web interface, like file uploads and edits, and will not be used for merge commits. Instead a special address %s can be used to associate commits with your account. Note that changing this option will not affect existing commits.
+keep_email_private_popup = Your email address will not be shown on your profile and will not be the default for commits made via the web interface, like file uploads, edits, and merge commits. Instead, a special address %s can be used to link commits to your account. This option will not affect existing commits.
 openid_desc = OpenID lets you delegate authentication to an external provider.
 
 manage_ssh_keys = Manage SSH keys