Woah, so much info =)
I don't think you need to manually build "QtCrypto" or Qca-qt5, the versions already available in Ubuntu's repos should be enough... I guess xD
That network redirection thing requires Qt 5.6, but you could just comment out that line, and you would just be losing the ability to get images inserted in posts whose links redirect somewhere else, so probably not much.
The std=c++11 thingie used to be manually specified prior to dropping Qt 4 support, but given the compiler and C++ standards requirements of Qt 5, I thought it was no longer necessary. I imagine your version of Ubuntu has a pretty old version of GCC or for some reason doesn't use c++11 or later as a default syntax.
I'm not sure all this work you're doing to get this to build will be worth it ^^