Minor stylistic and code changes for consistency

The most significant changes are:
* Removed underscore prefixes from wbLog??? supporting variables and functions (variables with a leading underscore are reserved as global identifiers by some implementations)
* Renamed variables to be consistent across the wbTime??? structures and functions
* Reflowed wbImport() so that comments are paired with the actions they're describing
* Increased tolerance for floating-point comparisons to three significant digits
Inserted checks for malloc() returning NULL in wbImport()
Replaced the while (...) loop in wbImport() with a for (...) loop that checks for writing past the bounds of the array
Wrapped the global variable gTimerInfoList in namespace wbInternal {}; renamed to timerInfoList
Moved sanity test of wbTimeType to wbClock_start() and wbClock_stop()
Implemented a check for wbTime_start() / wbTime_stop() timer pairing

The list member function std:find() returns wbInternal::timerInfoList.end() if no match is found; therefore, we need to check that the parameters passed in to wbTime_stop() correspond to an actual wbTimerInfo struct inserted by wbTime_start()