Uninitialized member variables - part 2

[fwesselm]

This is a follow-up to #1809:

• Initialize some more member variables
• Initialize some local variables
• Fix some warnings about unused / unreferenced parameters
• HiGHS now prints 1 generator(s) (instead of 1 generators) when symmetry detection identified one generator

Testing on 800+ MIPs showed that HiGHS behavior is not affected by these changes (as expected).