Different handling of form submissions inside workspaces

Problem/Motivation

Workspaces core adds validation handlers that prevent submission of any form that is not explicitly marked as safe via code from within a workspace. That also means that every time that an editor/site administrator needs to submit a form inside a workspace, a developer needs to mark the form as safe via code first, before forms can actually get submitted.

As discussed with Fabianx and amateescu, WSE should make this a bit easier by not denying form submission by default but rather prompting and warning the submitting user that the submissions happens inside a workspace.

Proposed resolution

When a form is submitted inside a workspace and not explicitly whitelisted on the settings form, a prompt asking the user for confirmation of the submission inside the workspace pops up and submission of the form happens only after hitting the confirmation button.

Certain forms may be whitelisted to not show the prompt. This happens via entering form ids on the WSE settings form. Further, some workspaces internal forms are hardcoded to never use the prompt as it doesn't make sense in this case.