Add ability to exclude tables from purge in ORM

[YaoOcelotl]

Tests for the filter schema expression if present in the DBAL connection and checks is the table name has been explicitly excluded.

[mikeSimonson]

What I was trying to say was that because the filter schema option is available in the connection configuration, you won't see any of the tables that are filtered out by the connection.

Thus there is no point in adding that feature in all the app that use doctrine. It's already there.

[YaoOcelotl]

The is filter expression regexp is used during create schema operations not during query's.

See setFilterSchemaAssetsExpression

[YaoOcelotl]

The idea for using the filter expression regexp is that if tables/views should not be considered during schema creation they also should not be considered during schema purge.

As an example i use ~^(?!view)~ to avoid overwriting view definitions.

[mikeSimonson]

@YaoOcelotl Thanks