Prevent IE errors on hidden login forms

In order to focus a field, it needs to be visible,
which can't be guaranteed on a core level by the login form JavaScript.
Optionally check for visibility via jQuery if it exists,
and allow explicit disabling of this behaviour via a unique identifier.
Merge pull request #3013 from silverstripe-iterators/pulls/login-form-js

Prevent IE errors on hidden login forms
Fixed reference to the templates documentation
Merge pull request #3023 from camfindlay/patch-5

Fixed reference to the templates documentation
Returning response from doChangePassword()
Merge pull request #3024 from silverstripe-iterators/pulls/changepw-return

Returning response from doChangePassword()
API Security.remember_username to disable login form autocompletion
Merge pull request #3020 from tractorcow/pulls/3.1-autocomplete-username

API Security.remember_username to disable login form autocompletion