Add number of females penned

[psolymos]

Adding the # inds (i.e. not just proportion): expose it as another argument (so user has to either use prop or number, but not both), and if the number is provided, it gives the prop as fpen.prop <- fem.pen.num/pop.start according to the original code.

If these args are vectors, then the prop or number ca change from year to year (last one used for all subsequent years).

• [x] Add option to pick prop or number,
• [x] allow prop or number to be a vector (dropping to 0 or keeping last value),
• [x] allow constant prop/number option in UI,
• [x] discuss how to allow vectorized option in UI.

[psolymos]

Mat pen and pred exclusion tabs are problematic when providing # females penned (especially multiple values for subsequent years): not clear how to calculate breakeven value.

[psolymos]

Vectorized # penned requires major rewrite: possibly additional tab or app.