Add force compaction and force split operations to UI and Admin

Would help debugging or at start of big upload or if we have a hot region we want to distribute over the cluster if we could just manually force the splitting of regions.

I thought it would be just a little messing in jsp but its a bit more than that.

Actual decision to split is made down in guts of the Store. Won't split if any references still around and a file must be > maxsize.

Chatting w/ Jon Gray, could set a flag on the region that we want to split. Could do this from UI (Can get to HRegion instance from HRS instance in HRS jsp). Stores have references to their hosting regions (I think). When figuring if we're to split, check the force split flag up in the hosting region.

To get the flag checked, safest way is to just force a flush (Otherwise, have to mess w/ locks in the compact/splitter thread). Registering a flush request on a region is easy enough to do. Its a public method on HRS (or HR).