Schema upgrade script.

Summary:
Created a script the runs all the necessary patches for db schema.
Stores information in the db about the latest patch that was applied.

Test Plan:
Created two test files '024.test.sql' and '023.test.sql' in this order.
'023' creates a database and '024' creates a table in this db. First ran
'./upgrade_schema.php 23' and made sure that patches were applied in order.
Then ran './upgrade_schema.php' to make sure db was up-to-date. Checked
manually from the db that the database and table exists.

Reviewed By: epriestley
Reviewers: epriestley
CC: jungejason, epriestley, tuomaspelkonen
Differential Revision: 115