Remove usage of Pimple class with new Pimple\Container class

Pimple 2 has a php-ext available, and if you use that instead of php version, then you get an exception in 
```class_alias('Pimple\Container', 'Pimple');``` since Container is no longer a user defined class. 
any usage of \Pimple is removed (Replaced with \Pimple\Container) in this PR.