waveform simulation selection persistence

[tomcl]

Describe the bug Waveform selection is not persistent across project open/close

To Reproduce There is also a small bug in the wave simulation. It appears that after changing the wave selection in a project and exiting, the next time the same project is opened (or due to other unknown conditions), Issie automatically deselects all waves.

Expected behavior Waveform selection should be persistent across project open/close

Additional context This is mostly desirable but could in some cases be annoying, e.g. it will encourage too many waveforms in selection which makes for performance and usability problems. Also, it might make bugs in waveform persistent (if there are any).