Use Doctrine SchemaManager to generate diffs instead of hard-coded SQL queries

- Made UUID char fields 'fixed' in Doctrine Schema
- Added check if the configured table exists in the current Schema before creating it
- Decouple Schema from Persistence
- Small Cs fixes
Merge pull request #21 from tPl0ch/eventstore-redesign-schema-adapter

Use Doctrine SchemaManager to generate diffs instead of hard-coded SQL queries