feat(graphing): automatically select distinct function names, e.g. f(x), g(x), ...

[Bnyro]

closes #50

[SuhasDissa]

Everything works fine,
I only found one (minor) issue with this.

When I add a function f(x), and then a function g(x) , the next suggested function would be h(x). However, if I remove the f(x) function from the list causing the list length to become 1, the next suggested function name will be g(x).

[Bnyro]

Hmm, you're right, it would be best to automatically "update" all existing function names when removing one, so that we always only have f(x), g(x), ...?

[SuhasDissa]

That'll work