Address widows in partnership terminations process

[ANBurdett]

See an unrealistic increase in partnership termination among the elderly.
Attribute this to not differentiating between cases in which a partnership dissolves and when a partner dies.

[ANBurdett]

Adjusted the dependent variable of the partnership termination process to account for cases in which a partner dies.

In the process of investigating widow status, noticed we have some observations for recently deceased individuals. Decided to maintain the observations but include a flag ("flag_deceased"), which we use to omit these observations from the estimation samples.