prusa3d
Replaced PyQt4 with PyQt5
Because PyQt4 is dead - only PyQt5 binary packages are available on most platforms anymore from pip and who wants to struggle to build PyQt4? Upgrading is definitely prudent at this point if PursaControl isn't officially dead already (is it? it sure seems that way).
With that said however, this PR is incomplete. The shaders fail to compile with error QOpenGLShader::compile(Vertex): ERROR: 0:1: '110' : version number not supported on Windows.
Cura recently switched to a newer version of Qt with the only apparent change that older systems are now excluded from running it, https://github.com/Ultimaker/Cura/issues/4466. So I'd say there needs to be a good reason to update Qt.
That issue appears to be with Qt 5.9/5.10 not necessarily older versions like Qt 5.8 or before. Probably safe to upgrade to Qt 5.8, but no point in bothering since PursaControl is just as dead as Qt 4 is.
The upgrade to Qt 5.9 was necessary for Cura due to a crash in the file dialogue for some Windows users. If there is a similar sort of bug in your Qt 4 version there is little chance for it to get fixed any more now, so I'd say that is a good reason to upgrade to a newer version. But do consider that you will drop support for some platforms by doing so. For instance, Qt5.7+ doesn't support Windows Vista any more.
