Allow to configure number of upfront tasks

[wvengen]

As a foodcoop admin, I'd like to be able to configure how much weeks upfront upcoming tasks are shown, instead of the default 7.

[wvengen]

[wvengen]

Suggestion from Stephan:

I think it would be helpful if the tool calculates how many tasks are created and until when. This makes it easy to understand/doublecheck the values you just entered.

I suggest to have the program print a sentence below like this:

-----------------------------------
Periodic Tasks
Period:          „7“ days +/-
Create upfront:  „49“ days +/-
Will create „7“ tasks from today until „23.02.2015“
------------------------------------

(I marked variables in „“; +/- means, you can enter values here)

[wvengen]

Hi Stephan, thanks for your suggestion. I think this would be useful! As I'm a bit short on time, I'd like to leave it with this, if it solves your problem. Does it?

[wvengen]

p.s. a short explanation is shown when you hover with the mouse over the input field

[wvengen]

Fixed by #331.