Update messages.json

This is my re-write attempt for the text displayed to a user who has just installed Floccus.  Current text has always confused me, so I hope you find this re-write helpful.

It would require one other code change, which is to make `Import` be displayed next to the appropriate icon in the menu.

Here is the rough idea oh how the text could look:
`+ Add Profile` `[->] Import`

_locales/en/messages.json

@@ -403,10 +403,10 @@
     "message": "This profile was deleted"
   },
   "LabelNoAccount": {
-    "message": "No profiles here"
+    "message": "No profiles yet"
   },
   "DescriptionNoAccount": {
-    "message": "Create a new profile to sync your bookmarks or import profiles from a different device or browser."
+    "message": "Add new & existing profiles, or Import from a file, then you can begin syncing."
   },
   "LabelLoginFlowStart": {
     "message": "Sign in with Nextcloud"
@@ -418,7 +418,10 @@
     "message": "Nextcloud login failed"
   },
   "LabelNewAccount": {
-    "message": "New Profile"
+    "message": "Add Profile"
+  },
+  "LabelNewImport": {
+    "message": "Import"
   },
   "LabelNestedSync": {
     "message": "Nested profiles"