Mortgage Interest Rates  added just slightly to yesterday's improvements, inching just a bit lower into the best levels in more than 6 months.  The bond markets that dictate rates took their cues this morning from central bankers as the heads of the US Federal Reserve and European Central Bank both offered some reassurance to bond market investors.  In the afternoon, a weak auction of 30yr Treasury Bonds prevented any further improvement, but not before quite a few lenders released positively revised rate sheets.   The most prevalently quoted conforming 30yr fixed rate for best-case scenarios moved closer to 4.125% for the first time since late October 2013, though 4.25% is very close.