Add new vendor namespace

[MauricioFauth]

• Renames the Facebook vendor namespace to PhpWebDriver (including classes with @deprecated annotation).
• Adds class aliases for Facebook vendor namespace.
• Adds @deprecated annotation for classes with Facebook vendor namespace.

Related to https://github.com/php-webdriver/php-webdriver/pull/914.

The new files in the src directory are used by Composer to generate its class maps. And the fully qualified \false is required in PHP 5 to ensure it is a dead code, since it can be overwritten in PHP 5.

[MauricioFauth]

As I mentioned earlier in https://github.com/php-webdriver/php-webdriver/pull/914:

I don't think this need to be in a new major version, since it has no backwards compatibility breaks. It can be added to 1.12.0 for example. And the @deprecated annotations will help users to easily change to the new namespace without issues. Then the Facebook vendor namespace could be safely removed in 2.0.0. Or a hard deprecation could be added in 2.0.0 with trigger_error and then removed in 3.0.0.

[OndraM]

I'm closing this PR, because its not feasible to keep this branch up-to-date, its already full of conflicts... However this PR would definitely serve as an inspiration once we will actually do the namespace change. Thanks @MauricioFauth!