Add more tests

[Marius786]

ADD GITIUM UNITTESTS FOR:

• [ ] wp_content_is_versioned

• [ ] gitium_enable_maintenance_mode

• [ ] gitium_disable_maintenance_mode

• [ ] gitium_get_versions

• [ ] _gitium_commit_changes

• [ ] _gitium_format_message

• [ ] _gitium_ssh_encode_buffer

• [ ] gitium_get_webhook

• [ ] gitium_admin_init

• [ ] gitium_get_keypair

• [ ] _gitium_generate_keypair

• [ ] gitium_get_webhook_key

• [ ] gitium_group_commit_modified_plugins_and_themes

• [ ] gitium_commit_and_push_gitignore_file

• [ ] gitium_merge_and_push

• [ ] gitium_acquire_merge_lock

• [ ] gitium_release_merge_lock

• [ ] gitium_update_versions

• [ ] gitium_check_after_event