Upgrade to vue3 (#16)

* upgrade to vue 3.x and framework7 8.x
* change calendar plugin to vue-datepicker
* disable export button when user does not hava any transaction
* implement new pin code input
* append thousands separator in amount in exchange rates page

postcss.config.js

@@ -0,0 +1,5 @@
+module.exports = {
+  plugins: {
+    'postcss-preset-env': {},
+  },
+};