Bug 22404: Fix parameter "for" of labels in subscription add form

Bug 22404: Fix parameter "for" of labels in subscription add form

Attribute "for" of tag labelshould contain input id, not name.

Test plan:
1) Go to serials -> add subscription second step
2) Click on labels of these three fields:
    - First issue publication date
    - Subscription start date
    - Subscription end date

--> without patch, nothing happen
--> with path, the datepicker is shown

Signed-off-by: Séverine QUEUNE <severine.queune@bulac.fr>
Signed-off-by: Séverine QUEUNE <severine.queune@bulac.fr>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>