add sqlite migrations

we move our PostgreSQL specific migrations to a subdirectory.
The SQLite migrations have been created by running `diesel` against a
copy, and then fixing what's broken.
In the end i reduced all modifications to a single create, since we
*are* starting out fresh with SQLite.

n.b.: i'm not entirely happy with the results yet, because diesel
heavily modifies our `plume-models/src/schema.rs`.
I'll keep fiddling until we have the same types between the two
databases.

migrations/postgres/2018-07-25-165754_refactor_notifications/down.sql

@@ -0,0 +1,8 @@
+-- This file should undo anything in `up.sql`
+ALTER TABLE notifications ADD COLUMN title VARCHAR NOT NULL;
+ALTER TABLE notifications ADD COLUMN content TEXT;
+ALTER TABLE notifications ADD COLUMN link VARCHAR;
+ALTER TABLE notifications ADD COLUMN data VARCHAR;
+
+ALTER TABLE notifications DROP COLUMN kind;
+ALTER TABLE notifications DROP COLUMN object_id;

migrations/postgres/2018-07-25-165754_refactor_notifications/up.sql

@@ -0,0 +1,8 @@
+-- Your SQL goes here
+ALTER TABLE notifications DROP COLUMN title;
+ALTER TABLE notifications DROP COLUMN content;
+ALTER TABLE notifications DROP COLUMN link;
+ALTER TABLE notifications DROP COLUMN data;
+
+ALTER TABLE notifications ADD COLUMN kind VARCHAR NOT NULL DEFAULT 'unknown';
+ALTER TABLE notifications ADD COLUMN object_id INTEGER NOT NULL DEFAULT 0;