Add an indicator for characters left before hitting the limit

Changes introduced:

1. A request to /api/statusnet/config.json is being made so that we fetch the text limit, site name and whether the registrations are open from the backend.
2. The aforementioned info was removed from /static/config.json
3. A number indicating the amount of characters left before hitting the text limit is being displayed.

I have returned.

src/components/post_status_form/post_status_form.js

@@ -94,6 +94,18 @@ const PostStatusForm = {
     },
     customEmoji () {
       return this.$store.state.config.customEmoji || []
+    },
+    statusLength () {
+      return this.newStatus.status.length
+    },
+    statusLengthLimit () {
+      return this.$store.state.config.textlimit
+    },
+    hasStatusLengthLimit () {
+      return this.statusLengthLimit > 0
+    },
+    charactersLeft () {
+      return this.statusLengthLimit - this.statusLength
     }
   },
   methods: {