Implement caching for actions that occur outside of the update log

[tensorc]

The update log (updates / writes) grants us a fair amount of fault tolerance, as we can simply abort and retry processing at a later time. However, some functionality would be too convoluted through this mechanism, such as pulling the pillory vote status or share link. In these cases, we will retry the request a reasonable number of times and should abort processing in the event of failure, but we could mitigate some opportunity for failure by caching results (even if only for very short periods of times, such as processing all lock logs).

There are various places throughout the code marked as TODO with a notation to cache responses, but I haven't investigated which of these are actually good candidates.