Multidimensional basis and other improvements

[GabrielePisciotta]

• Numerov is now a class (precedently known as Schroedinger.cpp): you can instantiate a Numerov solver object and then use it passing the proper potential object. You can save wavefunction and probability to a file using the proper method, also you can directly print everything evaluated, also the energy, simply calling std::cout << solver (where solver is a Numerov object). It can handle separable potentials, so you can use it with multidimensional basis. (need tests!)
• Potential class can now manage multidimensional basis (at the moment, considering only separable potentials), instead of taking only monodimensional vectors in input. Now you can also save the potential to a file, calling the proper method. Little changes such as using an enum instead of strings to define the type.
• Created a new main executable, where you can run examples such as box, finite well and harmonic oscillator.
• Fixed tests to be consistent with all the improvements

[Pandry]

Some minor tweaks that in my opinion should be at least noted, if not discussed...

[AndreaIdini]

Please see the comments

[AndreaIdini]

This method should take wave function as input

[GabrielePisciotta]

The wavefunction is an object property, so the method take it using this->

[AndreaIdini]

this as well

[GabrielePisciotta]

The probability is an object property, so the method take it using this->

[AndreaIdini]

prefer spaces to tabs for ASCII compatibility.

Way better to print all together

x (from the basis)         waveFunction         Probability
0.000000                    1.234e-10            2.012e-20
0.100000 ...
...

Could be made into a easy issue for @Bhez

[AndreaIdini]