Modernize random generation

[bodand]

In a lot of places, the project uses the C rand() function, even though the project itself is C++11, which has the "new" and fancy <random> header.
C++11 and up projects should always use <random> and one of its PRNGs instead of the severely limited C random functions, whose actual randomness is really platform-dependent and will work differently across libc implementations. Also using modulo to calculate a distribution skews the results. See this talk from STL, in which he describes why rand() is bad. (And also how to use the C++11 <random> header.)

I suggest a small random wrapper function be made that takes a min and max and generates a random number within those. Something like this:

int random_int(int min, int max) {
    static std::mt19937 rng(std::random_device{}());
    std::uniform_int_distribution<int> dist(min, max);

    return dist(rng);
}

And then use this function in all places where randomness is needed.