Make all images for Java Concurrency chapters smaller if too big

[preslavmihaylov]

One type of problem is that often times, images appear on the same line as the previous row as in here:

This can be fixed by putting a whitespace between the picture and the line before it.

Another problem is that often times, some images are rendered too big by default. example:

I think this one can be reduced to be at most 300 pixels wide

[ved-asole]

Hi @preslavmihaylov, let me know if I can take care of the above issue.

[preslavmihaylov]

of course, please go ahead!