Http request/response handler refactoring.

HTTP Request handler now manages HTTP request and response.

* added methods to manage HTTP response headers
* added methods to manage response body
* added accessors API methods for request parameters and
  response headers and body

Conflicts:
	src/mapserver/qgswmsserver.cpp

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Removed python plugins define

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ASTYLE formatting

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Restored streaming capabilities, added mHeadersSent flag and accessor

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Merge pull request #1671 from elpaso/requesthandler-refactoring2

Requesthandler refactoring2