Improve handling of application log line prefixes

[benhalstead]

The meta-data printed in front of each line of application logging (e.g 15/Apr/2019:13:44:23 Z DEBUG [grncQueryManager] ) is controlled by:

• The config file facility/config/logging.json
• The builder facility/builder/logger/builder.go
• The file logging/format.go and its associated test

The original concept was that an application could choose from a set of 'preset' prefixes or specify their own. In reality, there is one a default preset and if the application wants something different they need to provide their own format.

This change is to:

• Remove the concept of presets
• Move the definition of the default prefix out from the constant logging.PresetFormatFramework and into configuration at LogWriting.Format.PrefixFormat

There is also a bug where it is impossible to set empty string as the prefix which is definitely a foreseeable use-case. The ideal fix here is to change logging.LogMessageFormatter.PrefixFormat to *types.NilableString

[benhalstead]

This involves removing public member variables - not suitable for a minor release. Moving to 3.0.0