Export hydrodynamics as Excel sheets

[cailadd90]

Description of what's changed:

• function to export hydrodynamics as excel sheets added.

What needs doing:

• [ ] Incorporate the export function into fun_data of the hydro_v2 branch.

[mcwimm]

• [x] include Excel or csv as option in output settings
• [x] when csv is chosen download several files for summary stats. instead of excel with multiple sheets
• [x] settings box default: collapsed = F

[mcwimm]

Solved in PR #13