[Schema change] Add webseed support (BEP-19) (#317)

Store webseeds in Trackers table with is_webseed flag
Adjusts torrent creation accordingly

migrations/versions/ffd23e570f92_add_is_webseed_to_trackers.py

@@ -0,0 +1,24 @@
+"""Add is_webseed to Trackers
+
+Revision ID: ffd23e570f92
+Revises: 1add911660a6
+Create Date: 2017-07-29 19:03:58.244769
+
+"""
+from alembic import op
+import sqlalchemy as sa
+
+
+# revision identifiers, used by Alembic.
+revision = 'ffd23e570f92'
+down_revision = '1add911660a6'
+branch_labels = None
+depends_on = None
+
+
+def upgrade():
+    op.add_column('trackers', sa.Column('is_webseed', sa.Boolean(), nullable=False))
+
+
+def downgrade():
+    op.drop_column('trackers', 'is_webseed')