[FEAT] add cache busting via static_url_for and settings.cache_version (#1964)

closes #1954
this PR add cache busting to `/static`
additionally i combined `lnbits/core/static` with `lnbits/static`, it was not necessary and added a lot of duplicate code for cache busting. now you have to include all static files inside the html files with `{{ static_url_for("static", "app.css" ) }}`

Co-authored-by: Vlad Stan <stan.v.vlad@gmail.com>
Co-authored-by: Pavol Rusnak <pavol@rusnak.io>

lnbits/static/js/index.js

@@ -0,0 +1,36 @@
+new Vue({
+  el: '#vue',
+  mixins: [windowMixin],
+  data: function () {
+    return {
+      disclaimerDialog: {
+        show: false,
+        data: {},
+        description: ''
+      },
+      walletName: ''
+    }
+  },
+  computed: {
+    formatDescription() {
+      return LNbits.utils.convertMarkdown(this.description)
+    }
+  },
+  methods: {
+    createWallet: function () {
+      LNbits.api.createAccount(this.walletName).then(res => {
+        window.location = '/wallet?usr=' + res.data.user + '&wal=' + res.data.id
+      })
+    },
+    processing: function () {
+      this.$q.notify({
+        timeout: 0,
+        message: 'Processing...',
+        icon: null
+      })
+    }
+  },
+  created() {
+    this.description = SITE_DESCRIPTION
+  }
+})