Add more latex names for number fields

[rvisser7]

For some families of number fields $K$, we give a "pretty" latexed name for $K$ at the top of the field homepage, currently implemented for quadratic fields $\mathbb{Q}(\sqrt{D})$, biquadratic fields $\mathbb{Q}(\sqrt{A}, \sqrt{B})$, and cyclotomic fields $\mathbb{Q}(\zeta_n)$. This PR extends the field_pretty function to give latexed names for some additional families of number fields. :)

The following three cases have been added:

• General multi-quadratic fields $\mathbb{Q}(\sqrt{D_1}, \sqrt{D_2}, \dots, \sqrt{D_k})$ : For fields $K$ of degree $2^k$ with $2^k - 1$ quadratic subfields, this now selects the $k$ smallest quadratic subfields $Q(\sqrt{D_1}), \dots, Q(\sqrt{D_k})$ which generate $K$.

  http://localhost:37777/NumberField/8.0.12960000.1
  http://localhost:37777/NumberField/16.0.63456228123711897600000000.10
  http://localhost:37777/NumberField/32.0.4026692887688564776141139207792885760000000000000000.1

• Imprimitive (non-biquadratic) quartic fields $\mathbb{Q}(√ (A + B \sqrt{D}))$: This checks if a quartic field $K$ has exactly one quadratic subfield $\mathbb{Q}(\sqrt{D})$, and then computes a generator for $K$ of the form $√(A + B \sqrt{D})$ by factoring the defining polynomial for $K$ over $\mathbb{Q}(\sqrt{D})$. If $A = 0$, then returns the latexed form as a pure quartic field $\mathbb{Q}(\sqrt[4]{n})$.

  http://localhost:37777/NumberField/4.0.512.1
  http://localhost:37777/NumberField/4.2.2048.1
  http://localhost:37777/NumberField/4.4.2048.1

• Pure cubic fields: $\mathbb{Q}(\sqrt[3]{n})$: Detects if a cubic field K is of the form $\mathbb{Q}(\sqrt[3]{n})$, by computing a real root of the defining polynomial for $K$.

  http://localhost:37777/NumberField/3.1.108.1
  http://localhost:37777/NumberField/3.1.243.1
  http://localhost:37777/NumberField/3.1.300.1

As always, any comments/feedback very welcome! 🙂