Remove :compile_path from config and move it to Mix.Project
Ensure app key is required when getting the compile_path
Extract Mix.ProjectStack from Mix.Server
Move mix configs to app environment and split TasksServer
Do not override builtin type
Compile not ok dependencies on deps.get and deps.update
Move mix dependencies to _build
Rename fetched to loaded and add a manifest_path
Sinplify mechanism for checking and handling locks

In particular, there is no need to pass :lockfile around deps.
We also remove the umbrella handling from the lock.
Ensure archives work with new _build setup
Move rebar and other deps to _build
Share _build path when running commands from umbrella
Ensure rebar dependencies are stored in the proper directory
Improve coverage for builds and rebar integration
Update new applications .gitignore
Rename _build to _build/shared
Add mix iex that simply fails and tell users to use iex -S mix
Allow builds to be customized per environment
Prune tasks when build per environment is on
Ensure we can clean deps that no longer exists