[JS] Split form and non-form modals and support custom modal footers

[MaximeBICMTL]

Description

This PR refactors the LORIS modal to make two major changes:

• Separate form and non-form general modals into separate reusable components.
• Make modal footers optional and allow consumers to provide their own footer for the generic modal.

Architecture

• The Modal component from jsx/Modals.tsx is split into three components:
  • Modal: The general non-form modal, which allows the consumer to provide the body and optionally the footer.
  • FormModal: The form modal, which is similar to the current modal and provides form and submit logic/controls.
  • ModalFrame: common architecture between the two modals, technically FormModal could also be made to depend directly upon Modal but this would require some higher-order component machinery because the form body and content should both be wrapper in a form element, and this wrapper is undesirable in the general case.
• The styling relies less on bootstrap and more on flexbox for layout.
• The modals can be scrollable, not sure if that was the case before or not.

Examples

[TODO: provide videos]