Add a basic main page with login

None of the links work and the marketing copy sucks, but it's just
showing the bones while I figure the technical bits out.

response.go

@@ -0,0 +1,31 @@
+package main
+import (
+	"net/http"
+)
+
+// Custom ResponseWriter to track Content-Type
+type customResponseWriter struct {
+        http.ResponseWriter
+        contentType string
+        wroteHeader bool
+}
+
+func (crw *customResponseWriter) WriteHeader(code int) {
+        crw.wroteHeader = true
+        crw.ResponseWriter.WriteHeader(code)
+}
+
+func (crw *customResponseWriter) Header() http.Header {
+        return crw.ResponseWriter.Header()
+}
+
+func (crw *customResponseWriter) Write(b []byte) (int, error) {
+        if !crw.wroteHeader {
+                if crw.contentType == "" {
+                        crw.contentType = http.DetectContentType(b)
+                        crw.ResponseWriter.Header().Set("Content-Type", crw.contentType)
+                }
+                crw.WriteHeader(http.StatusOK)
+        }
+        return crw.ResponseWriter.Write(b)
+}