DB schema change desires

[jrochkind]

I intentionally did not make any DB schema changes in Umlaut in the 4.0 release, in order to keep the upgrade to 4.0 as easy as possible.

But there are a number of schema changes that have suggested themselves. I would like to try to bundle them all together in one future Umlaut upgrade with one migration. @scotdalton and others, please feel free to add to this list.

• ServiceResponse.url is 1024 chars. It needs to be much longer, or text
• ServiceResponse.display_text should also potentially be longer
• Request tries to keep a serialized HTTP_ENV hash in one column. It should not do this, but should take out the individual ENV/headers it needs in separate columns, each of which need to be 4096 or longer or just text. One of these should definitely be the original request path.
• Permalink should keep the original request path in a string (new column), not just reconstruct it from a referrer
• Referent has some 'mirror' columns directly in the referents table, that really duplicate values in associated referent_values. This was meant to be an aid for debugging and/or efficiency for finding 'equivalent' referents, but has not been used, and makes logic more complicated to keep them in sync. Remove them.

Future Umlaut version will distribute with TWO migrations, a non-destructure one (that you can run while still running old Umlaut, it does not remove any data columns old Umlaut needs but may add some additional ones), and a second destructive one that removes those columns (to be run after upgrade is complete). Second migration will not be installed automatically. To make upgrade with no downtime easier.