Add pagination to project API

The project API used `nil` as `page` and `per_page` parameters. So there was no way to get all project with API if there was more than 100 projects.

This MR fixes this by adding `params[:page]` and `params[:per_page]` to the `Project.from_gitlab` call. The parameters are still optional (if there are undefined, it just send `nil`).

It affects the API routes:
`GET /projects`
`GET /projects/owned`