core

Replace go-logging with a zap based implementation. The implementation
is mostly compatible with the legacy format but differs in a two key
ways:

1. CRITICAL and NOTICE log levels no longer exist. Calls to Critical get
   mapped to error and NOTICE gets mapped to INFO. The methods
   associated with these levels will be removed in a future CR.
2. The log level constants are now sourced from the zap/zapcore packages.
   These values are incompatible wit the go-logging constants. Please be
   sure to use the appropriate constant when necessary.

The existing go-logging package is still used by the chaincode shim to
reduce the risk of negatively impacting legacy chaincode.

Change-Id: Iaf5fac807244883a8285892ccd350c5256959782
Signed-off-by: Matthew Sykes <sykesmat@us.ibm.com>