Implemented basic HTTP message header parsing.
Rewritten HTTPServer to split into cHTTPConnection, cHTTPRequest and cHTTPResponse classes.
Split cHTTPConnection implementation into a separate file.
Fixed parsing and implemented write nofitication.

The web connection finally works with a browser.
Fixed leaking HTTPRequest objects
Added cHTTPServer callbacks; fixed keep-alives.

The HTTP server now calls callbacks specified in its start function (debugified atm.) and it processes multiple requests on a single connection.
Added UserData to cHTTPRequest.

Callbacks may store one pointer of per-request data in the cHTTPRequest object. The object doesn't touch this data (doesn't own it).
Added URLDecode() and ReplaceAllCharOccurrences() to StringUtils.
Created basic cHTTPFormParser.

It can parse forms in the application/x-www-form-urlencoded encoding, used for forms without file uploads.
Fixed recognition of multipart-form-data forms.
Improved the HTTPFormParser code.

No change to the functionality.
Added StrToLower(), URLDecode() and ReplaceAllCharOccurrences().
Added cNameValueParser.
Added cEnvelopeParser and cMultipartParser.
Fixed MultiPartParser's boundary parsing.
HTTP Server can now parse multipart/form-data forms; better architecture.
Added Basic auth support to cHTTPRequest.
cHTTPConnection sends Content-Length with HTTP errors, too.
Fixed Base64Decode() returning wrong value.
WebAdmin uses the new HTTP functionality.

This is a partial implementation of #183.