Split none-core extensions to there own repository

                   
|Q            |A  |
|---          |---|
|Bug Fix?     |no |
|New Feature? |no |
|BC Breaks?   |not at the moment|
|Deprecations?|no |
|Tests Pass?  |yes|
|Fixed Tickets|#12|
|License      |MIT|

Todo:

- [x] Doctrine DBAL
- [x] Doctrine ORM
- [x] JMS Metadata
- [x] Symfony DI extension
- [x] ~~Symfony Validator extension~~ (keep this in the core)
     
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