Merge lp://staging/~sumanah/postorius/bug-1157947 into lp://staging/postorius

This branch fixes bug # 1157947 by finding all user-visible occurrences of hard-coded English strings in the src/postorius/templates/postorius/ directory and templatizing them as follows:

  {% trans 'English message' %}

(In this branch I also made three very trivial grammar, spelling, and capitalization fixes to the templates.)

Templates I inspected (in many cases no change was needed):

base_ajax.html
base.html
confirm_dialog.html
domain_confirm_delete.html
domain_index.html
domain_new.html
errors/
    generic.html
lists/
    confirm_delete.html
    confirm_remove_role.html
    held_messages.html
    index.html
    mass_subscribe.html
    memberoptions.html
    members.html
    metrics.html
    new.html
    settings.html
    subscribe.html
    subscriptions.html
    summary.html
    unsubscribe.html
login.html
menu/
    general.html
    info.html
    list_nav.html
    maintanance.html
    mm_user_nav.html
    settings_nav.html
    subscriptions.html
    user_nav.html
    user_options.html
    users_nav.html
more_info_display.html
site_settings.html
user_address_activation.html
user_address_activation_link.html
user_address_activation_sent.html
user_address_preferences.html
user_mailmansettings.html
user_profile.html
user_settings.html
user_subscription_preferences.html
user_subscriptions.html
user_tasks.html