Add AJAX profiling support for MooTools

I started using MiniProfiler on a rails project that uses MooTools instead jQuery. Ajax calls were displayed only after page reload so I added this changes to make it work.

Note that I have 3 failing tests when i run `bundle exec rake spec` but I don't have memcached installed.

```bash
Finished in 0.71693 seconds
116 examples, 3 failures

Failed examples:

rspec ./spec/components/memcache_store_spec.rb:17 # Rack::MiniProfiler::MemcacheStore page struct storage can store a PageStruct and retrieve it
rspec ./spec/components/memcache_store_spec.rb:27 # Rack::MiniProfiler::MemcacheStore page struct storage can list unviewed items for a user
rspec ./spec/components/memcache_store_spec.rb:35 # Rack::MiniProfiler::MemcacheStore page struct storage can set an item to viewed once it is unviewed

```