Add dev-tools for debugging work on freedesktop-sdk

We've often been frustrated by the lack of tooling when trying to debug issues in builds, as we don't have anything useful in the bst shell environment. This adds a stack element which can be used to add useful tools into the build environment. Currently it only includes vim, which this MR also adds, but later MRs could be created to improve this.

The proposed workflow is to simply add dev-tools.bst as a (build) dependency of whatever element is giving you grief, and then having access to the tooling in the bst shell environment.