Port 'Project selection widget' setting (project_issue_autocomplete)

Actually, change of plan. We still need this setting for #1044950: Re-architect the project-dropdown UI selector on node/add/project-issue to prevent server crashes, although maybe it should just live in project itself? It'd be shared with both project_issue and project_release that way (since we also have the same UI problem at node/add/project-release, although d.o doesn't expose that page).

I suppose this could still be a node-type setting instead of site-wide. However, maybe that's overkill, and we could just get away with a site-wide global for this.

There's also a somewhat wonky "Project navigation" block that d.o doesn't use, but that'd care about the same thing. Another reason to just have this in project (if we keep that functionality at all).

Can you explain your reasoning here? I'm not sure it makes sense to have this per-project-node-type. You combined two half-baked proposals of mine into a single cake that doesn't seem like it's going to work at all. ;) For example, /node/add/project-issue is potentially including choices across multiple project node types. It's a single UI. I fail to see how we can reconcile a setting on each of those project types to figure out the UI to use. Seems like a mess.

Either this needs to be a setting tied to the [project-issue] node type in the URL, or it needs to be a global site-wide default. But a setting tied to each project type seems like the worst of both worlds. ;)

Also, just moving the setting around doesn't actually give us the autocomplete, etc. This issue is about porting the functionality, not just the setting UI itself.
Edit: see comment #8.

Thanks,
-Derek

Note: I forgot we already had #1044950: Re-architect the project-dropdown UI selector on node/add/project-issue to prevent server crashes open about using this setting to control the UI at node/add/[issue-node-types] so we can leave that part out of the patch here.

Committed/pushed #5 to project_issue.
Cleaned up the titles and descriptions of the menu items a bit (Sentence case instead of Always Caps, etc) and committed/pushed #9 to project.

Thanks, and sorry for the delays!
-Derek