Return Riak type (EE/OSS) in /explore/clusters.

[travisbhartwell]

Adds the "riak_type" key to the cluster info list.

Checks to see if the cluster is Riak EE by seeing if the
riak_repl_console module is available.

Fixes #93 (in part). Does not add riak_version as indicated in discussion in #93.

[travisbhartwell]

This is the sample output, from Riak EE:

$ curl http://localhost:9000/explore/clusters/default
{"cluster":{"id":"default","riak_node":"[email protected]","development_mode":true,"riak_type":"ee"},"links":{"self":"/explore/clusters/default"}}

From Riak OSS:

$ curl http://localhost:9000/explore/clusters
{"clusters":[{"id":"default","riak_node":"[email protected]","development_mode":true,"riak_type":"oss"}],"links":{"self":"/explore/clusters"}}

[dmitrizagidulin]

Tested out the branch, works great. Thanks Travis! +1 from me.