fix(Chat): Allow for case insensitive pubkey replacement

When entering a user name like `@Pascal` it wouldn't be properly replaced
with the pubKey of `pascal.stateofus.eth` since it was comparing to `@pascal`

This commit ensures simple user name mentions are properly matched against
their ens names regardles of their case.

Fixes part of #769

src/app/chat/view.nim

@@ -104,7 +104,7 @@ QtObject:
   proc replaceMentionsWithPubKeys(self: ChatsView, mentions: seq[string], contacts: seq[Profile], message: string, predicate: proc (contact: Profile): string): string =
     result = message
     for mention in mentions:
-      let matches = contacts.filter(c => "@" & predicate(c) == mention).map(c => c.address)
+      let matches = contacts.filter(c => "@" & predicate(c).toLowerAscii == mention.toLowerAscii).map(c => c.address)
       if matches.len > 0:
         let pubKey = matches[0]
         result = message.replace(mention, "@" & pubKey)