Added the check of the api_key to be able to pass the IP check and import remotely with only the API key.

Separate remote import page from user imports ...

Due to complexities of trying to have both user-initiated imports and
remote imports handled in the same page, the import process has been
split into two separate use cases.  pages/import.php is now specifically
for use by the remote import process, while pages/repo_import_latest.php
remains for usage by authenticated MantisBT users.

This will require that all cronjobs or post-commit hooks that triggered
a remote import be updated to point to the new import url.  Framework
version has been bumped accordingly.