fix default component schema attrs

[inf-rno]

• the defaults weren't working correctly because it was trying to call Kernel.function_exported? with binary strings instead of atoms
• so it would always present the Bandit.Pipeline as default
• adds checks similar to the form validation
• driveby fixes Gettext deprecated compiler warning

p.s.: I am an elixir noob. so i'm likely not following some convention

[inf-rno]

cc @TheFirstAvenger

[inf-rno]

friendly bump

[inf-rno]

bump again grazie