Account creation user experience/Strings

These are the message changes involved in improving the login and create account forms. In the switch to the new forms  in  and subsequent changes, the following message keys changed.

The earlier "ACUX" experiment involved other string changes, particularly from validation; for that, see /Experiment subpage.

SpecialUserlogin.php messages removed

 * userlogin -> either a specific 'createaccount' or 'login' in page heading and title
 * userloginnocreate -> gone. It was previously "Log in" (to distinguish from "userlogin", which was "Log in / create account").  This is no longer necessary since the login page heading and title is now always login-only.
 * gotaccount & gotaccountlink -> gone, we let the user login from the link in the top-right navigation
 * nologin & nologinlink -> gone, login form has a fancy userlogin-joinproject 'Join [wiki]' message.

Userlogin template messages removed

 * userlogin-resetlink -> userlogin-resetpassword-link (needs to be brief)
 * yourname -> userlogin-yourname without colon (in both forms)  (MessagesQqq said it's used in Preferences, but I don't see it)

Usercreate template messages removed

 * yourpasswordagain -> userlogin-yourpasswordagain without colon (MessagesQqq said it's used in Preferences, but I don't see it)
 * createaccountreason -> createacct-reason without colon

Userlogin template messages changes

 * remembermypassword -> userlogin-remembermypassword (and gone from createacct) BUT still in use in Special:ChangePassword
 * mailmypassword -> gone, users are always sent to a form to recover password BUT still in use in Special:ResetPassword
 * yourpassword -> userlogin-yourpassword (in both forms) BUT still in use in Preferences

Usercreate template message changes
(These messages are still used by preferences.)
 * createaccount -> createacct-submit button (and message that appeared in h2) BUT still in use in the skin
 * youremail -> createacct-emailrequired and createacct-emailoptional BUT still in use in Preferences
 * yourrealname -> createacct-realname BUT still in use in Preferences
 * new form eliminates the prefsectiontip div tip:
 * prefs-help-email-required is redundant with the placeholder text
 * Doesn't show the wordy prefs-help-email
 * Doesn't show the wordy prefs-help-email-others

TODO
TODO remove the colon from yourdomainname.

TODO? have we tested securelogin-stick-https

TODO Could/should rename showCreateOrLoginLink and createOrLoginHref, since the only link shown is login's [Join wiki].