[WIP] Add stability on real and imaginary axis

[kivvix]

• add stability on negative real axis
• add stability on imaginary axis
• make a function to compute box where compute stability function
• improve viewer to show $x_{max}$ and $y_{max}$
• add Github action to make a Github pages with viewer ?
• improve viewer with React.js or View.js ?

Because I create this branch from my branch of fixing splitting methods and add tests, I also have all other commits...