Switch to DTCS for hint storage

The DateTieredCompactionStrategy is a good choice for HintedHandoff so that we reduce the compaction load we incur when users build up hints. atobey@datastax.com and others have tried the following patch in various setups and have seen significantly less load from hint compaction.

https://gist.github.com/tobert/c069af27e3f8840d137d

Setting the time window to 10 minutes has shown additional improvement.

krummas do you have any feedback about this idea and/or settings?