3.0 constants

Refs #5452, #5451 

This makes Cache packages usable as standalone without requiring constant CACHE. Since it depends on Core package I added DS constant there.

Another package which requires similar treatment is Log. I don't think system temp dir is a good default for logs so better to just remove use of LOGS constant and have user always specify path for FileLog.
Since this is a standalone package it makes sense not to check for debug.