Fix getting settings default result

[magicrub]

This adds a new GetDecimal() helper but also it ensures the default value is returned when a TryParse() fails in the various helpers.

Current code assumes TryParse(string, result)==false does not touch result because we are initially setting the result with the default value and then always return the value without checking the return boolean. However, the docs say it will trample on result when returning false. Here's the docs for Int32.TryParse()

       //   result:
        //     When this method returns, contains the 32-bit signed integer value equivalent
        //     of the number contained in s, if the conversion succeeded, or zero if the conversion
        //     failed. The conversion fails if the s parameter is null or System.String.Empty,
        //     is not of the correct format, or represents a number less than System.Int32.MinValue
        //     or greater than System.Int32.MaxValue. This parameter is passed uninitialized;
        //     any value originally supplied in result will be overwritten.
        //
        //  public static bool TryParse(string s, out Int32 result);