Improve task level plot

Following modifications have been added:

• new colormap
• grid
• labels are rotated by 90 degrees now
• fix a small bug where the highest level has not been plotted

For comparison, here's the default output of the current version of the script:

And here is the modified version:

Additionally, I added the -c and -d flags.

• -c: counts on how many levels each task operates, and writes it in brackets on the task name label
• -d: if a task has the same number of counts for multiple levels, displace the counts by a tiny amount to make them visible.

Here's an example output: Now we can for example see that there is more than one level of grav_down_in with 8 tasks calls.