Replace of LibCurl by QtNetwork

* Updated CMake files
* Created FileDownloader class using QtNetwork
* Removed libcurl use
* Updated tests

(closes OpenFLUID/openfluid#198)
Replace of LibXml2 by QtXml

* Modified FluidXDescriptor methods
* Modified DistributionTables methods
* Updated CMake files
Merge branch 'develop-qt' of https://github.com/chataignerm/openfluid into chataignerm-develop-qt