(core) start applying defenses for untrusted document uploads

Summary:
This applies some mitigations suggested by SQLite authors when
opening untrusted SQLite databases, as we do when Grist docs
are uploaded by the user.  See:
  https://www.sqlite.org/security.html#untrusted_sqlite_database_files

Steps implemented in this diff are:
  * Setting `trusted_schema` to off
  * Running a SQLite-level integrity check on uploads

Other steps will require updates to our node-sqlite3 fork, since they
are not available via the node-sqlite3 api (one more reason to migrate
to better-sqlite3).

I haven't yet managed to create a file that triggers an integrity
check failure without also being detected as corruption by sqlite
at a more basic level, so that is a TODO for testing.

Test Plan:
existing tests pass; need to come up with exploits to
actually test the defences and have not yet

Reviewers: dsagal

Reviewed By: dsagal

Differential Revision: https://phab.getgrist.com/D2909

app/server/declarations.d.ts

@@ -100,3 +100,7 @@ declare module '@gristlabs/pidusage' {
 }
 
 declare module "csv";
+
+declare module 'winston/lib/winston/common' {
+  export function serialize(meta: any): string;
+}