Reviewed addition to db table prefix

Review of #2935

- Removed from .env files and added warnings for use if found in config
  file.
- Updated permission service to use whereColumn queries to auto-handle
  use of prefixes.

app/Config/database.php

@@ -69,6 +69,9 @@ return [
             'port'           => $mysql_port,
             'charset'        => 'utf8mb4',
             'collation'      => 'utf8mb4_unicode_ci',
+            // Prefixes are only semi-supported and may be unstable
+            // since they are not tested as part of our automated test suite.
+            // If used, the prefix should not be changed otherwise you will likely receive errors.
             'prefix'         => env('DB_TABLE_PREFIX', ''),
             'prefix_indexes' => true,
             'strict'         => false,