This change converts redundant attribute assignments of the form `a =
a;` or `a = someSet.a;` into cleaner `inherit` statements. This reduces
verbosity and follows common Nix style for bringing attributes into
scope.
Statix Codes: W03 (manual_inherit), W04 (manual_inherit_from)
Also include statix and the rule in our configuration.
Instead of having to manually stub packages that should not be
downloaded we instead automatically stub all packages (except a small
list of whitelisted ones). Tests can re-introduce the real package by
using the `realPkgs` module argument.
Sometimes plugins doesn't follow the form
```
addSbtPlugin("${plugin.org}" % "${plugin.artifact}" % "${plugin.version}")
```
for instance
```
addDependencyTreePlugin
```
This commit allow free form plugin dependency.
