[WIP] Modify schema, creation of new attributes

Added some new attributes changes in the Member and Mailing List model
This Merge Request is work-in-progress

• Now I am following Mark's Implementation, see here,here and here for Mark's implementation.

src/mailman/database/alembic/versions/58858f75303c_added_new_bounce_attributes.py

+"""Added new bounce attributes
+
+Revision ID: 58858f75303c
+Revises: 2d2d0ef0828f
+Create Date: 2019-06-28 01:10:48.210528
+
+"""
+
+
+import sqlalchemy as sa
+
+from alembic import op
+from mailman.database.helpers import exists_in_db, is_sqlite
+
+# revision identifiers, used by Alembic.
+revision = '58858f75303c'
+down_revision = '2d2d0ef0828f'
+
+
+def upgrade():
+    # ### commands auto generated by Alembic - please adjust! ###
+    if not exists_in_db(op.get_bind(), 'address', 'bounce_info'):
+        op.add_column('address', sa.Column('bounce_info', sa.PickleType(),
+                                           nullable=True))
+    with op.batch_alter_table('domain') as batch_op:
+        batch_op.create_unique_constraint('uq_domain_mailhost', ['mail_host'])
+    # ### end Alembic commands ###
+
+
+def downgrade():
+    # ### commands auto generated by Alembic - please adjust! ###
+    if not is_sqlite(op.get_bind()):
+        op.drop_column('address', 'bounce_info')
+        op.drop_constraint('domain', 'uq_domain_mailhost')
+    # ### end Alembic commands ###