Rationalize schema manager naming

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | no
| Tests pass?   | yes
| License       | MIT
| Doc PR        | fridge-project/dbal-docs#5

This PR rationalizes platform naming:

 * Rename all `getTable*` methods to `get*`
 * Rename all `getGenericTable*` methods to `getGeneric*`