HTML Export: option to merge Flow/To associations and flows, or all links

[Guillaume]

Wtih a generated HTML site, the properties page of an element shows a number of tabs based on the available traceability: Associations To, Associations From, Flow To, Flow From, Other Links.
Other links gathers all "other" links in any direction.
Whilst this decomposition can be handy, it would be useful to select an option to generate the relations tabs:
- Default = current behaviour
- Associations, Flow, Other Links = merge Flow to and Flow from to a single tab, same for the associations
- Single tab = everything in one tab e.g. Links