Pick 1 of 3: (weak) Don't print only these warnings which totally flood the terminal.

Don't print only these warnings which totally flood the terminal: 'deprecated-copy', 'int-in-bool-context'. Print all others.

---- (the text below is present in all 3 MRs to chose from).

We had an example in Deepak's merge request, that flooding the compilation log with warnings is not useful at all. It was impossible to see what the error is, because the compilation log was too large, and gitlab clipped it. So I propose three solutions here:

• weak !269 (closed) - don't print only these warnings that totally flood the terminal
• middle !270 (closed) - only print two warnings: maybe uninitialized (I think it's useful) and #warning pragma (because we use it!).
• strong !271 (closed) - only print #warning pragma (because we use it!).

The maximally enabled warnings (which I did two months ago) are still maximally enabled, I mean that all possible warnings are turned into errors, depending on library versions and depending on compiler version. For some older libieigen versions I had to turn off some warnings as errors. They were still printed. In this MR they are not printed anymore - but only when older libeigen is used (e.g. ubuntu 16.04). But it is enabled as error on newer libeigen (e.g. ubuntu 18.04).

I make three MRs here, so that we can pick the most useful one.

It is an MR into branch fixExtraWarnings where I enabled float conversion warning, which is necessary to properly start using long double and float128 precision in place of Real.