webui: Renamed themes dir to ui

- Eliminated intermediate bootstrap dir

ui/templates/root/index.html

@@ -0,0 +1,12 @@
+{{define "title"}}Inbucket{{end}}
+
+{{define "script"}}{{end}}
+
+{{define "menu"}}
+<div id="logo">
+  <h1><a href="/">inbucket</a></h1>
+  <h2>email testing service</h2>
+</div>
+{{end}}
+
+{{define "content"}}{{.greeting}}{{end}}