Flexible ID tags

[sukhwinder33445]

resolves #85

• change upgrade schema file name

[julianbrost]

The schema upgrade script will probably have to be renamed as well before merging the PR. But as far as I can tell, the corresponding changes that will be needed in notifications-web were not started yet, were they? (So I don't want to say it will be the next one and should use 016.sql yet.)

[julianbrost]

Changes look good so far from just looking over the code. I'll continue with testing once a corresponding web PR is ready (so that I don't break my test setup while doing so).

[julianbrost]

@yhabteab Can you do me a favor and test this, especially in conjunction with Icinga/icinga-notifications-web#133?

Also, in case anyone needs it, I already have a SQL snippet lying around to roll back that schema change:

ALTER TABLE object ADD COLUMN host text, ADD COLUMN service text;
UPDATE object SET host = (SELECT value FROM object_id_tag WHERE object_id = id AND tag = 'host');
UPDATE object SET service = (SELECT value FROM object_id_tag WHERE object_id = id AND tag = 'service');
ALTER TABLE object ALTER COLUMN host SET NOT NULL;
DROP TABLE object_id_tag;

Changes requested were done, the Go part looks fine so far but I'm waiting on the PHP part for a final review