Freeze goals and activities when scrolling

[jpacios]

Hi!

Thanks a lot for this fantastic tool.

When you have a big feature map it is difficult to place features in the good column, you have to scroll up and down, or create the feature and then drag and drop it. It would be nice if the first part (personas, goals, activities) could be 'frozen' so that the scroll only affects the tons of features below.

Hope you find this useful!