- also making sure unlocking works fine

Tests have broken as locks were expanded and auto-filled newer versions
of lockfiles. This fixes them back.

- the internal representation for package locks moves from `{Name, {pkg,
  PkgName, Vsn}, Lvl}` to `{Name, {pkg, PkgName, Vsn, Hash}, Lvl}`
- the internal representation for packages moves from `{pkg, PkgName,
  Vsn}` to `{pkg, PkgName, Vsn, Hash}`
- the hash can be `undefined`, meaning no check will be done
- no checking is done yet.

Add more version constraints

Allow for any number of whitespaces after compairison opperator

Improve updating and error printing

Fix failing tests

- The rebar package index files have been moved off the default path and
  will require a new `rebar3 update`
- Caching of downloaded packages automatically takes place in a path
  relative to the CDN used
- The cache path is not shared with hex as we now write and modify data
  in there arbitrarily
- Basic tests plus the working set for more of them is included