GUAC-1176: Provide user with help text during login. Style continuation dialog differently. Add continue button.

guacamole/src/main/webapp/app/login/styles/input.css

@@ -38,4 +38,13 @@
 .login-ui .login-dialog .buttons input[type="submit"] {
     width: 100%;
     margin: 0;
-}
+}
+
+.login-ui.continuation .login-dialog .buttons input[type="submit"] {
+    width: auto;
+}
+
+.login-ui.initial .login-dialog input.continue-login,
+.login-ui.continuation .login-dialog input.login {
+    display: none;
+}