Add support for project.json config file to bolt build.

@markhibberd can you review?

Implements the bulk of project.json functionality for bolt build. Includes:
- src
- output
- build
  - config
  - inline-main
  - inline-register
  - entry-points
  - entry-groups

Also adds a -p|--project flag to allow specifying the location and name of the project json file (default 'project.json' in the project root). Does correct fallback of command-line argument, then project.json, then hard-coded default.

Also renames the -r/-n inline flags and removes the -i flag.

Couple of TODOs came out of this:
- What to do about the -m|--modules flag? I've left it in there for now, without any project.json support (would be simple enough to add if we want to keep this flag).
- entry-points and entry-groups project.json fields take complete file paths at the moment, as that is what the command line flags take. Seems like we should change them to be module ids at some point though. The original project.json spec we wrote had them as module ids, I assume resolved against the project config js. This is outside the scope of this work anyway, so I've left it as-is for now, when/if we come back and change this for the script flags, it should automatically just work in project.json as well.