Add a store_ts method to Logger1

This adds another store_ interface that takes a series of metrics and stores them with a timestamp.

Time will be assumed to come from a corrected source elsewhere, and a signal will be sent with the logdata in it as well, thus it is not for serious batch usage.

However, when buffering a set of keys and then transmitting them at once, it should be fine, and the overhead of passing a single array of one item vs. a single item function is neglible and thus I picked a batch interface.