Add Spearator to make UI clearer

[tronta]

When I was using Grada for the first time, I was confused what this is doing:

I always though it was belonging to some settings of the upper selected tools.

When playing around I discovered it is actually adding a background. So I would really encourage to add an own headline to it:

I know you are adding a further headline, when one of the entries is selected, but I also find this kind of confusing, as it's adding an unneeded separation between the tool and it's settings.

Not sure, what's your take on it.

[kjozsa]

I like it, it's similar to my suggestion of using collapse-able panels for these parts, and the expand/collapse state could be saved per the user's preference. . I have actually implemented this in PR #224