Rename camel_imapx_list_response_get_mailbox().

Rename to camel_imapx_list_response_get_mailbox_name().

I'm working on an actual CamelMailbox class and don't want get_mailbox()
functions to be misleading.
Rename camel_imapx_status_response_get_mailbox().

Rename to camel_imapx_status_response_get_mailbox_name().

I'm working on an actual CamelMailbox class and don't want get_mailbox()
function to be misleading.