Liberate cassandra.yaml parameter names from their units

The arbitrary units have bugged me for too long.

I would like to see, instead of trickle_fsync_interval_in_kb=1024 trickle_fsync_interval=1MiB, and instead of max_hint_window_in_ms = 3 * 3600 * 1000, max_hint_window=3h

We aren't currently even consistent, with counter_cache_save_period not specifying its units, and stream_throughput_outbound_megabits_per_sec=200 is tremendously ugly (vs inter_dc_stream_throughput_outbound=25MiB/s or inter_dc_stream_throughput_outbound=200MBit/s)

This is really trivial, and would make our config file look a lot less ugly. Of course, we'll have to support both in parallel for a period.