Fix warnings if callbacks are not set

[lukasbableck]

I initially noticed this problem in AddressBook.php when editing an address in the frontend (see stacktrace below). I have also changed all other places where this problem could occur.

Stacktrace:

ErrorException:
Warning: Undefined array key "onsubmit_callback"

  at vendor/isotope/isotope-core/system/modules/isotope/library/Isotope/Module/AddressBook.php:240
  at Isotope\Module\AddressBook->edit('...')
     (vendor/isotope/isotope-core/system/modules/isotope/library/Isotope/Module/AddressBook.php:107)
  at Isotope\Module\AddressBook->compile()
     (vendor/contao/core-bundle/src/Resources/contao/modules/Module.php:214)
  at Contao\Module->generate()
     (vendor/codefog/contao-haste/library/Haste/Frontend/AbstractFrontendModule.php:52)
  at Haste\Frontend\AbstractFrontendModule->generate()
     (vendor/isotope/isotope-core/system/modules/isotope/library/Isotope/Module/Module.php:116)
  at Isotope\Module\Module->generate()
     (vendor/isotope/isotope-core/system/modules/isotope/library/Isotope/Module/AddressBook.php:79)
  at Isotope\Module\AddressBook->generate()
     (vendor/contao/core-bundle/src/Resources/contao/elements/ContentModule.php:98)
  at Contao\ContentModule->generate()
     (vendor/contao/core-bundle/src/Resources/contao/library/Contao/Controller.php:623)
  at Contao\Controller::getContentElement(object(ContentModel), 'main')
     (vendor/contao/core-bundle/src/Resources/contao/modules/ModuleArticle.php:197)
  at Contao\ModuleArticle->compile()
     (vendor/contao/core-bundle/src/Resources/contao/modules/Module.php:214)
  at Contao\Module->generate()
     (vendor/contao/core-bundle/src/Resources/contao/modules/ModuleArticle.php:70)
  at Contao\ModuleArticle->generate(false)
     (vendor/contao/core-bundle/src/Resources/contao/library/Contao/Controller.php:551)
  at Contao\Controller::getArticle(object(ArticleModel), false, false, 'main')
     (vendor/contao/core-bundle/src/Resources/contao/library/Contao/Controller.php:393)
  at Contao\Controller::getFrontendModule('0', 'main')
     (vendor/contao/core-bundle/src/Resources/contao/pages/PageRegular.php:194)
  at Contao\PageRegular->prepare(object(PageModel))
     (vendor/contao/core-bundle/src/Resources/contao/pages/PageRegular.php:61)
  at Contao\PageRegular->getResponse(object(PageModel), true)
     (vendor/contao/core-bundle/src/Resources/contao/controllers/FrontendIndex.php:320)
  at Contao\FrontendIndex->renderPage(object(PageModel))
     (vendor/symfony/http-kernel/HttpKernel.php:163)
  at Symfony\Component\HttpKernel\HttpKernel->handleRaw(object(Request), 1)
     (vendor/symfony/http-kernel/HttpKernel.php:75)
  at Symfony\Component\HttpKernel\HttpKernel->handle(object(Request), 1, true)
     (vendor/symfony/http-kernel/Kernel.php:202)
  at Symfony\Component\HttpKernel\Kernel->handle(object(Request))
     (public/index.php:44)