Update branding to µPaaS by @sneak

Change all references from "upaas" to "µPaaS" in page titles,
headers, and README. Add attribution link to sneak.berlin in
the navigation bar.

templates/login.html

@@ -1,12 +1,12 @@
 {{template "base" .}}
 
-{{define "title"}}Login - upaas{{end}}
+{{define "title"}}Login - µPaaS{{end}}
 
 {{define "content"}}
 <div class="min-h-screen flex items-center justify-center py-12 px-4">
     <div class="max-w-md w-full">
         <div class="text-center mb-8">
-            <h1 class="text-3xl font-medium text-gray-900">upaas</h1>
+            <h1 class="text-3xl font-medium text-gray-900">µPaaS</h1>
             <p class="mt-2 text-gray-600">Sign in to continue</p>
         </div>