(mu-cite-get-prefix-register-verbose-method): Move function to mu-register.el.

(mu-cite-get-prefix-register-verbose-method): Move function to mu-register.el.
(mu-cite-get-prefix-register-method): Likewise.
(mu-cite-get-prefix-method): Likewise.
(mu-cite-save-registration-file): Likewise.
(mu-cite-load-registration-file): Likewise.
(mu-cite-add-citation-name): Likewise.
(mu-cite-get-citation-name): Likewise.
(mu-cite-minibuffer-history): Move variable to mu-register.el.
(mu-cite-citation-name-alist): Likewise.
(mu-cite-registration-symbol): Likewise.
(mu-cite-registration-file-modes): Likewise.
(mu-cite-registration-file-coding-system-for-write): Likewise.
(mu-cite-registration-file-coding-system-for-read): Likewise.
(mu-cite-allow-null-string-registration): Likewise.
(mu-cite-registration-file): Likewise.
(mu-cite-registration-file): Move macro to mu-register.el.

(TopLevel): Add autoload setting for `mu-cite-get-prefix-method',
`mu-cite-get-prefix-register-method' and
`mu-cite-get-prefix-register-verbose-method'.