Bug 37982: Replace edit form with GET

Bug 37982: Replace edit form with GET

Caught by tests from bug 37728

 # $VAR3 = 'koha-tmpl/intranet-tmpl/prog/en/modules/serials/serials-collection.tt:158';

We don't really need the form to be POSTed, we should not reach the URL maxlength.
The UI will certainly explode if there are lot of items to edit anyway.
The code is not clear on this page as we are sending several forms using
the items selected from this table. But this one form is used to display
the edit form and so can be GET (and better as the URL can be shared).
The other actions have their own form (in modals mostly).

Test plan:
Create a subscription and go to the serial collection page.
Make sure at least one item is select and click the "Edit" button.
No behaviour change expected here, the edit form should still be
displayed.
Try the other actions on top of the table and confirm they are still
working as before.

Signed-off-by: Phil Ringnalda <phil@chetcolibrary.org>
Signed-off-by: Pedro Amorim <pedro.amorim@ptfs-europe.com>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>