Proper build dependencies

[bycruz]

Add buildDependencies which should be the only dependencies that a build.lua script has access to. Useful to not include these in sea final outputs.

[bycruz]

Unlike #28, I now know this is definitely necessary as there's a distinction between dev dependencies and build dependencies that does admittedly get muddy for some languages like javascript.

[bycruz]

If I do end up sandboxing build scripts to only provide the lde-build api, then this will become obsolete