BC break: removed deprecated `PackageVersions\Versions::ROOT_PACKAGE_NAME` constant

[Ocramius]

…

This simplifies the tool to no longer be a plugin: PackageVersions\Versions is now a much simpler class that is no longer generated/written to disk at installation, and ocramius/package-versions is no longer a "type": "composer-plugin", but rather a more usual "type": "library" package.

This:

• Fixes #138 - this library no longer changes vendor post-installation
• Fixes #142 - the rootPackage version is now detected via composer, and no longer leads to changes in vendor/ocramius/package-versions/src/PackageVersions/Versions.php at each change of source root in a project
• Fixes #152 - when "lock": false is used in composer, since we no longer access lock file information from sources of this package
• Fixes #107 - writing to vendor is no longer happening from this library, so no file access rights should be needed.

[Ocramius]

Will probably need to remove some error suppression from the current tests to see why they're failing :shrug:

[Ocramius]

Curious failure:

Changed current directory to /tmp/InstallerTest5f3fd3c3450612.54650718/global
Loading composer repositories with package information
Updating dependencies
Lock file operations: 1 install, 0 updates, 0 removals
  - Locking ocramius/package-versions (1.0.0)
Writing lock file
Installing dependencies from lock file (including require-dev)
Package operations: 1 install, 0 updates, 0 removals
  - Downloading ocramius/package-versions (1.0.0)
  - Installing ocramius/package-versions (1.0.0): Extracting archive
Plugin initialization failed (Plugin ocramius/package-versions could not be initialized, class not found: PackageVersions\Installer), uninstalling plugin
  - Removing ocramius/package-versions (1.0.0)
    Install of ocramius/package-versions failed

In PluginManager.php line 209:

  Plugin ocramius/package-versions could not be initialized, class not found:  
   PackageVersions\Installer                                      

I think I'll kill off the whole e2e installer test :shrug: