build: Moving OTP to its own Maven module, refactor out Raptor into its own module

[trygvis]

TL; DR: This turns OTP into a multi-module project. Discussion required.

Summary

This changes the project from being a single-module setup to have multiple Maven modules. There was consensus for changing the build to this at the OTP Berlin developer days, this is an attempt to do that.

There was also an agreement to move Raptor out of the core module so that has been done at the same time. In order to get it done, a few files was moved to a shared framework module. The classes that are there are the bare minimum to get Raptor to compile.

Note that since this PR moved around all source file, this PR will most likely mess up many other PRs that will have to be rebased so choose when it is integrated with caution.

Questions:

• Where should the modules live? Now they live in a folder called modules/. The main code live under modules/otp, Raptor is under modules/raptor.
• Module/folder naming.
• This change more or less changes every source code file in the project, so after the merge it would be advisable to add the commit id to /.git-blame-ignore-revs.
• The framework module. Should it be renamed to lang, utils or something similar? I think it would be nice to separate it from the framework package that is inside OTP, both in name and package name.

Future TODOs:

Clean up the dependency list.

Recommendation: keep all dependencies in the dependency management section in /pom.xml. Use properties to manage the version across group IDs as it is done today. Remove any version tag from child modules.

Apply useful Maven plugins

• https://www.mojohaus.org/versions/versions-maven-plugin/index.html
• https://maven.apache.org/enforcer/maven-enforcer-plugin/

Look to see if there are any useful rules from the Enforcer plugin that you want applied. In particular the requireSameVersions rule might be useful: https://maven.apache.org/enforcer/enforcer-rules/requireSameVersions.html.

Documentation

No documentation is updated in this PR. Should definitely be done later.