Automation of the threshold level for finding cell nucleus

[carandraug]

Different possible approaches to this:

• show user the result of threshold value and give option to change the value. Repeat until user is satisfied
• fit histogram to a function (maybe a double gaussian) to indentify the background and nucleus peaks
• start at high threshold values and measure size of the obtained nucleus. Slowly increase until the difference on its area is really big (alternative, make big jump, and cut the diference into half, until finding the best value)