Fix #1787(logging): create gridUtil.logDebug, comment out all debug

Refer #1787 for discussion, but essentially create a native ui-grid logging capability (`gridUtil.logDebug`, `gridUtil.logWarn`, `gridUtil.logError`), which just wraps $log.  Include in uiGridConstants variables to turn these on and off.

Ideally medium term the build process for distribution would set `LOG_DEBUG_MESSAGES` to false, but that's not critical at this time as this commit also comments out all debug messages.