Review the drag and drop filter handling specification

[romaintailhurat]

When a component is moved via drag and drop in the questionnaire view, the specification for handling filters is the following:

a. if the component is not a member of any filter, do nothing
b. if the component is the first and last member, delete the filter
c. if the component is the first member, replace it by the next element sharing its type (anywhere in the questionnaire)
d.if the component is the last member, replace it by the preceding element sharing its type (anywhere in the questionnaire)

I falsely identified the case b. as a bug (see the archived issue).

Nonetheless, it appears quite brutal.

To smooth things a bit, we may propose an alternative behavior, vaguely outlined by:

• let the filter in place, whatever the target location
• if the filter is nonsensical (eg the condition question is inside the filter block), we may alert the designer, and tag the filter as deactivated (and thus we won't propagate it when sending the payload for generation)

[romaintailhurat]

I need to describe the integrity checks we want for filters.