1. Why is this change neccesary?
White text on a yellow background was illegible with most terminal color schemes
2. How does it address the issue?
The white text was replaced with a bash compatible dark gray while keeping the
yellow background colour
3. What side effects does this change have?
Resolves#1552
Otherwise, caller needs to invoke WriteHeaderNow himself after
AbortWithStatus(), which is error-prone.
Also modified ErrorLoggerT() such that it always writes log to response
body. Otherwise calling AbortWithStatus() will fail to write body because
c.Writer.Written() is set true by WriteHeaderNow().