Improved the Climatic >Prepare>Length of Season dialog

[MeSophie]

Fixes #9402
@rdstern @N-thony I replaced the Up-Down control with the Day Range sub_dialog in the Length of season dialog. Please have a look.

[rdstern]

@MeSophie that's absolutely the right idea. But:
a) Can you make the receiving control narrower - it just has the day number so can be much smaller.
b) I'm happy that you adapted the control like that. But there are 2 problems:

1. The data uses the shifted year, while you are not using that here. So 30 April should be about day 305 starting from 1 July.
2. You have messed up the settings too generally, see below:

I went back to the start of the rains, and now can't do the start day here either. The length dialog should not affect the control for any other dialog.

[MeSophie]

@rdstern Please can you test the dialog again?

If this is related with Length of season dialog then I'm not sure that the range day can recognize the shifted year since we don't have any DOY receivers here.

[rdstern]

@MeSophie I am very sorry, as you have now stopped the interaction between the controls on the dialogs. But I have now thought of a much simpler way of doing this! And it is sufficiently different that - if you and @lilyclements agree, then I suggest you close this pull request and start again on the length dialog.
It is working well and here is an example for Zambia:

So it is doing fine, except, with your current control I had to pretend the season was finishing on 31 October. (It actually was 30 April which is day 305 in the shifted year - which you don't give!)

Notice 305 is the day I want and it is there in the End_season_filled variable! Hence my new suggestions:

a) Add another receiver, with label End_Filled
b) Complete these controls with defaults where you can from the names. For the start it should be easy. For the end use end season as the defaults, and end rains otherwise.
c) For the End_Filled, that is only available for the end of the season. Fill that control if you are able.
d) The Length More checkboa is disabled unless End_Filled is not empty.
e) The Length_More checkbox becomes like the 2 controls above. So with length_more as the default name.
f) There is no day_range control at all. Instead use max(End_Filled) as the day number you need. This will either be correct, which corresponds to FALSE in the end Season, or it won't matter, because it won't be used, i.e. there are no FALSE rows in the End and hence no More rows in the length!

Very sorry for the extra work, but I like this solution much more!

[rdstern]

@MeSophie you didn't read my suggestions above enough. I was amazed you changed the dialog sao quickly and no saw you didn't. I strongly suggest you close this pull request and then you should find the new pull request is much easier to implement. Happy to chat over skype if you wish.