Schema integrity check improvements

- Create userdata tables and indexes that are missing
- Delete tables and triggers that should no longer exist
- Run schema integrity check before user data migration
- Run schema integrity check after restart error

This is meant to address two problems:

1) Database damage, and subsequent use of the DB Repair Tool, that
   results in missing tables

2) A small number of cases of schema update steps somehow not being
   reflected in users' databases despite their having updated userdata
   numbers, which are set within the same transaction. Until we figure
   out how that's happening, we should start adding conditional versions
   of schema update steps to the integrity check.

This is currently only running the update check after a restart error,
which might not occur for all missed schema update steps, so we might
want other triggers for calling setIntegrityCheckRequired().

test/tests/schemaTest.js

@@ -248,6 +248,14 @@ describe("Zotero.Schema", function() {
 			});
 		})
 		
+		it("should repair a missing userdata table", async function () {
+			await Zotero.DB.queryAsync("DROP TABLE retractedItems");
+			assert.isFalse(await Zotero.DB.tableExists('retractedItems'));
+			assert.isFalse(await Zotero.Schema.integrityCheck());
+			assert.isTrue(await Zotero.Schema.integrityCheck(true));
+			assert.isTrue(await Zotero.DB.tableExists('retractedItems'));
+		});
+		
 		it("should repair a foreign key violation", function* () {
 			yield assert.eventually.isTrue(Zotero.Schema.integrityCheck());