Initial solution and database update for #11

The database now contains a displayname_source field which is the
telegram user ID of the user whose point of view the displayname
is from.

Updates from the relaybot user always take precendence, but currently
the relaybot will never automatically fetch displaynames.

alembic/versions/bcfefa1f1299_add_displayname_source_fields_for_.py

@@ -0,0 +1,23 @@
+"""Add displayname source fields for puppets
+
+Revision ID: bcfefa1f1299
+Revises: bdadd173ee02
+Create Date: 2018-05-19 17:00:21.078098
+
+"""
+from alembic import op
+import sqlalchemy as sa
+
+# revision identifiers, used by Alembic.
+revision = 'bcfefa1f1299'
+down_revision = 'bdadd173ee02'
+branch_labels = None
+depends_on = None
+
+
+def upgrade():
+    op.add_column('puppet', sa.Column('displayname_source', sa.Integer(), nullable=True))
+
+
+def downgrade():
+    op.drop_column('puppet', 'displayname_source')