Improve logging output

[mwahle]

VDMS is not very verbose with respect to logging. Debugging can lots of guesswork and frustrating.

We would like to see

• configurable log levels
• more debugging output
• generic errors replaced with specific ones, like at failed transactions
• issue #63 addressed (reported separately because should be quick to implement and has high impact by itself)

[ifadams]

@cwlacewe We generally need to do an overhaul of logging in VDMS. Its a mess and wildly inconsistent, but its a big project at this point. Leaving open for future refinement and discussiomn.