DB migration, small technicalities.

* DB migration rewritten:
  * Migration scripts are embedded as FS.
  * Migration versions are handled automatically.
* Use generics in utils.

server/sql_schema/V1_init.sql

@@ -21,5 +21,3 @@ CREATE TABLE feature_photos (
   thumbnail_contents blob NOT NULL,
   contents blob NOT NULL
 );
-
-PRAGMA user_version = 1;

server/sql_schema/V2_proposals.sql

@@ -3,5 +3,3 @@ CREATE TABLE proposals (
   description text NOT NULL,
   how text NOT NULL
 );
-
-PRAGMA user_version = 2;