Fix/not linking truffle projects

[honestbonsai]

Fixes #1078

This PR does the following:

1. Fixes contracts_build_directory needing to be a direct child of build_directory (which defaults to ./build) to get a Truffle project to link.
2. Allows you to put your contracts_build_directory as deep as you want as a descendant of your Truffle project. (e.g. path/to/project/a/b/c/d/contracts_build_directory)
3. Allows you to put your contracts_build_directory outside of your Truffle project (i.e. not a descendant).

It does not do:

1. Handle the renaming of a contract in the directory. This seems like a current bug with Ganache. Currently in develop and this branch, if you rename a contract's file name, all other contracts in Ganache disappear. If you try to rename it back to the original name, nothing changes. I considered this out of scope, will open a new issue for this.
2. Subfolders of contract artifacts within contracts_build_directory. Didn't seem like it was in scope for this card. If enough people want it, then a new issue/feature request should be made.

FYI:

1. Does seem to be slightly slower than the current implementation, since I'm recursing through the chain of directories. My feeling is that most people will just have their contracts_build_directory inside their project anyways, so this shouldn't be too big of an issue, but if you think it is let me know.

[mikeseese]

Perhaps this and lines 97/98 (won't let met comment there) should not be using the basename function, and be more something like

path.join(head, filename) === path.normalize(this.project.config.contracts_build_directory)

I don't think it's an issue either way as startWatchingContracts() will check to see if the directory exists before watching. Food for thought

[mikeseese]

If tests pass, and you verified this solves the issue, and you have verified that it works with default settings still (it should), this LGTM!

My other comment is for you to decide if you want to change it or not. Either way, has my approval.

[honestbonsai]

Yup, tested with truffle unbox drizzle and it works out of the box (haha) and also default empty truffle-config.js.

[0xjjpa]

Just wanted to comment that I've tested this with truffle unbox react and it works as well. Finishing a course w/Solidity this weekend with it, talking about good timing!