reorganize project_nodeapi()

the fact that project_nodeapi() is a single hook being shared by both project_project and project_issue type nodes has already caused some confusion, and now, a critical bug (that was live on drupal.org for a few minutes): http://drupal.org/node/66146#comment-107953. that sucks. neither killes nor i noticed this particular problem, since the project code is so weird in so many ways. ;)

the attached patch fixes this confusion in hook_nodeapi(), by having project_nodeapi() (which will live directly in project.module, not project.inc) check the type of the given $node, and then call type-specific versions (project_project_nodeapi() in project.inc, and project_issue_nodeapi() in issue.inc) to do the real work. this will also solve http://drupal.org/node/65601

while i'm at it, i'm moving project_form_api() into project.module, to make it clear this is shared by all of the project module, not just project_project type nodes or something.