Add support for ad-hoc vulnerability scanning of BOMs

### Current Behavior:

In order to scan components for vulnerabilties, users have to create a project first. Projects are great for continuously scanning components, but they're too heavyweight for use cases where only a single scan is desired.

### Proposed Behavior:

Dependency-Track should support ad-hoc vulnerability scanning of components in a given uploaded BOM, *without* creating a project for it.

This is related to #374. But instead of having to check each component individually, uploading a BOM should suffice.