Generate random particles

[ezrayst]

Describe the PR Generate random particles within an element as first step to solve Issue #609.

General design of the random generator:

• Make a new class called QuadrilateralRandomQuadratures
• Update assign_quadrilateral in cell to include generator_type with default string value of "gauss"

Alternative design:

• Generate random quadratures in geometry but the design of the code would be rather messy

Things to do in this PR (this will notsolve issue #609 entirely)

• [x] Implement for 1, 4, 9, 16 and 25 particles per cell for quadrilateral element
• [ ] Implement for triangular and hexahedron (for completion)
• [ ] Test functions (note that random generator cannot be tested for locations of particles, but only the number of particles within the cell)

Things to do in next PR (to complete issue #609)

• [ ] Compute accurate gauss weights for each randomly generated particles
• [ ] Test functions on the computed weights

Example of generation of 25 particles per cell:

Example of generation of 4 particles per cell:

[kks32]

@ezrayst A discussion or a Request for comments is for discussion before a PR and would like for it to happen in an issue before we write code. PR shouldn't be the place where we have a general discussion of how to implement a new feature, especially when you have spent time coding it. I'm closing this issue, as this is not a possible way to solve the random point generation. We need more discussion so please open an RFC