Configurable SSL error details messages

Configurable SSL error details messages

This project adds support for a translatable and customisable error detail file
(errors/templates/error_details.txt). The file is stored like we store error
page templates today. Inside the file, an HTTP-like format used that can be
later extended to other error details (and beyond):

name: value
details: "value"
descr: "value"

or

name: value
details: "multi
     line
     value"
descr: "value with a \"quoted string\" inside"

The code supports future translations, just like Squid already support error
page translations.

This is a Measurement Factory project
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Some Technical details:
 - The errorpage code which is related to loading and parsing error templates
   moved to TemplateFile class. This class is used as base class for
   ErrorPageFile class which used to load error page templates.
 - The HttpHeader parser used to parse error details
 - The  error details for various languages cached to memory
 - The ErrorDetailsList  used to store a list of error details for a
   language/locale
 - The ErrorDetailsManager is a class used to load and manage multiple error
   details list (ErrorDetailsList objects) for many languages. It also
   implements a simple cache.