[DDC-1657] Prevent autoincrement sequences from creating DROP SEQUENCE statements because of old/new schema missmatch.

[DBAL-204] Sane refactoring of the previous idea. Removed a bunch of code again and implemented proper schema namespacing. Also got the wording right (hopefully) and fixed the algorithms.

DBAL-91 - Fix auto-generation of asset names (foreign keys and indexes) which could lead to exceptions due to auto-quoting of PostgreSQL for example. Now hashing the names with crc32+dechex

DBAL-54 - Fix sequence drop executed before tables, however sequences mostly depend on tables. Also clean up several test-failures on MSSQL tests and  Oracle Index detection.

DBAL-50 - Explicitly add an index for each foreign key added to a Schema\Table instance. Removed code to FixSchema based on foreign keys, since assumptions now dont apply anymore. Refactored algorithms to check for duplicate or potential overrule indexes into Schema\Index classes, added tests and unified Table API handling these conflicts