Change SchemaMigration ID type to number

[craicoverflow]

Motivation

Fixes #495

What

Change the ID type of SchemaMigration to match the ID type in the database.

Verification

Postgres

Postgres migrations should work as before.

SQLite

1. Install sqlite3 to the runtime example.
2. Change database configuration to:

"db": {
  "database": "sqlite3",
  "dbConfig": {
    "filename": "./db.sqlite"
  }
},

3. Executing migrations with SQLite should now work.

[wtrocki]

WDYT about moving runtime to sqllite?