Fix format-security warnings (again)

[morxa]

Use string literals in all format strings and cast to char * if necessary. Also include -Wformat, which is necessary if you want to use -Wformat-security.

See also #915 that did something similar.

[dorodnic]

Hi @morxa
Thank you, again, we will try to avoid these in the future

[morxa]

Thanks for merging! With the -Wformat fix, everyone should hopefully notice the problem earlier :)