tribler: 7.1.2 -> 7.4.0-exp1 (python 3)

Updating version for tribler to use python 3.
One most notable change is dropping the optional `pythonPackages.meliae`
as it does not support python 3 and addition pony, lz4 and pyqtgraph.

Also cleaned up a few other dependencies and removed an old workaround
for broken ui-graphics.