Small Bank vignette corrections

[damonbayer]

Two changes:

1. Typo in the first bank vignette.
2. The code to calculate number_balked yields 0, when five customers balk in the log. When a customer balks, their activity_time is 0, so I used this to count the number of balks. Maybe there is a better way to calculate this.

[Enchufa2]

Many thanks, but I'd prefer to add a leave activity, which sets finished to FALSE, and keep the calculation, as you can see in the commit above.