Update symmeplot

[tjstienstra]

I am making a new version of symmeplot, see #16 from symmeplot, with a few backward incompatible changes. Not a lot needs to change in BRiM. However, to fully fit the profile I am doing mainly one backward incompatible change in BRiM as well:

• First, it was the case that you had to provide the axes as the first argument when initializing the Plotter object. It has now become a keyword argument, where an axes is automatically created if none is provided.

[tjstienstra]

Note that the tests will probably crash because the update of symmeplot has not yet been released.