Combine dependency-related workspace methods

[benmccann]

There's also the dependencies field and the only thing we use it for is to check if eslint is installed. Ideally I think we could combine it with isResolveable or whatever we call it (#76). They work slightly differently though. I think that isResolvable will work in a monorepo, but it only returns true/false. dependencies only looks at the package.json, but will return the version. Ideally we create a method that returns a version and works in a monorepo

I also think that dependencies is a bit unclear in that it contains dependencies and devDependencies

[AdrianGonz97]

I also think that dependencies is a bit unclear in that it contains dependencies and devDependencies

we settled on combining them into a single dependencies field as we couldn't think of any use-case where knowing if a dep was installed as a dependency or a devDependency would be particularly helpful