Add polymer template checker

For details how to use it see the polygerrit-ui/README file.

Twinkie patch note: the template checker uses twinkie library for
checking. The library has a bug, that stops checker from working. As a
temporary workaround, the patch is added directly to this change. The
patch will be removed after fixing bug in twinkie library.

Change-Id: I3375d6654478e12eeb1df9a2b912125f6929838c
diff --git a/polygerrit-ui/app/.gitignore b/polygerrit-ui/app/.gitignore
index c235144..6b96e60 100644
--- a/polygerrit-ui/app/.gitignore
+++ b/polygerrit-ui/app/.gitignore
@@ -1,2 +1,3 @@
 /plugins/
 /node_modules/
+/tmpl_out/