Improve Profile-Handling

[Netroxen]

As a user,
I want to see my custom profile in the sidebar,
if the administrator is not using the default MemberData.

Acceptance Criteria

• It's done when the sidebar uses the custom member folder and member type to show user information
• It's done when the default user type is used as a fallback
• It's done when there's a method which registers a field as the avatar image
• It's done when there's a registry record to store the avatar image field value
• It's done when a log message is displayed if multiple fields are registered as avatar images.

Additional Information

• This should be implemented for the profile section in the sidebar template.
• The username can still be pulled from the currently logged-in user. i.e. the MemberData object

Technical Information

We should implement this similarly to how the dexterityindexer registers a searchable field...

dexteritytextindexer.searchable('eventtype')

eventtype = schema.Choice(
    title=_(u'event_contenttype_eventtype_title',
            default=u'Event Type'),
    description=_(u'event_contenttype_eventtype_description',
                  default=u'Please enter the type of the event.'),
    vocabulary=EVENTTYPES,
    default='',
    required=True,
)

Instead we should implement something like sidebar.avatar('my_custom_image').