Log view: cache logs for speedy re-access

[MetRonnie]

Problem

Sometimes loading log files can take a few seconds as it loads it over the network. Switching between job.out and job.err can be frustrating in this regard.

Proposed Solution

Have a FIFO cache of log files stored in CacheStorage (which we already use for storing workspace layouts).

The tricky part might be reconciling the cached log lines and incoming lines if more are written to the log file since the caching.