To reduce GConf usage in em-composer-utils.c:

- Relevant functions in em-composer-utils.c now take arguments for
  reply and forward styles.

- Redundant forwarding functions were removed:

    em_utils_forward_attached()
    em_utils_forward_inline()
    em_utils_forward_quoted()

- EMailReader now has "forward-style" and "reply-style" properties,
  which get bound to the appropriate EShellSettings properties in
  modules/mail/e-mail-config-reader.c.  These same EShellSettings
  properties are bound to the combo boxes in Composer Preferences.