feat: add apilayer as provider for fixer api (#127)

feat: add apilayer as provider for fixer api
feat: update exchange rate when saving api key

migrations/000006.php

@@ -0,0 +1,12 @@
+<?php
+// This migration adds a "provider" column to the fixer table and sets all values to 0.
+// It allows the user to chose a different provider for their fixer api keys.
+
+/** @noinspection PhpUndefinedVariableInspection */
+$columnQuery = $db->query("SELECT * FROM pragma_table_info('fixer') where name='provider'");
+$columnRequired = $columnQuery->fetchArray(SQLITE3_ASSOC) === false;
+
+if ($columnRequired) {
+    $db->exec('ALTER TABLE fixer ADD COLUMN provider INT DEFAULT 0');
+    $db->exec('UPDATE fixer SET provider = 0');
+}