Rounded legend icons

In case of a merge translations will have to be updated, because currently the squares are created by using HTML, which is part of the label text.

In this commit this is not the case anymore.

The strings to be translated are "Start", "Change", "Termination".

Currently:

"<span foreground='#000000' background='#aed581'> </span> Starting task"

"<span foreground='#000000' background='#fff176'> </span> Changing task"

"<span foreground='#000000' background='#e57373'> </span> Terminating task"