Fixed #147 Added NamespaceTokenFixer to fix unscoped namespace strings

[danielmorell]

Description of the change

This PR resolves #147. It contains two primary changes:

1. It adds a class NamespaceTokenFixer that walks through files token by token to fix namespaces in strings in the composer autoload files.
2. It adds a more robust way of testing by creating a plugin aptly named "conflict" that has dependencies that conflict with the Rollbar plugin when not properly scoped. If the conflict plugin can be activated and the tests pass the Rollbar plugin will be able to safely run in a WordPress installation with other plugins.

Type of change

• Bug fix (non-breaking change that fixes an issue)

Related issues

• Fix Fatal Error: Class name collision between main project's Psr\Log\AbstractLogger and Rollbar plugin's namespaced version #147

Checklists

Development

• Lint rules pass locally
• The code changed/added as part of this pull request has been covered with tests
• All tests related to the changed code pass in development

Code review

• This pull request has a descriptive title and information useful to a reviewer. There may be a screenshot or screencast attached
• "Ready for review" label attached to the PR and reviewers assigned
• Issue from task tracker has a link to this pull request
• Changes have been reviewed by at least one other engineer