Revert "Replace Underscore with custom _ (Util.js)"

This reverts commit cab99fb9a71723542d14c2b66493884970338185.
Added custom build of lodash (command to build is in the file)
Removed Shim.js from postal. Users should include a shim if they need to support e.g. IE8 (e.g. es5-shim.js or the provided custom one).
Added indexOf to shims