choosing reading direction for morphisms

[vinnylarouge]

it would be nice to be able to toggle bottom2top and left2right as options, especially since it seems that string-diagram reading direction is a matter of taste between different fields.

[vinnylarouge]

(i might just be a pervert, but recently I've been depicting string diagrams from left to right like they do in estonia)

[regular-citizen]

#953 gives the option to export to tikz with the left-to-right direction. In theory, there is no reason not to have a global flag in the settings that allows to toggle the reading direction.

In practice, doing this everywhere is a bit of work. For example, the slice control on the right would make no sense in left-to-right mode.