Add new coordinate fields when a marker is created

Rather than try to link markers with existing Point fields, the
submission form is now set to create new Point fields on
successful marker creation. These new fields are the same as the
regular Points fields, except these cannot be edited by the user,
and are tied to the original coordinates of the marker.

(However, editing the marker will not yet affect the associated
Point fields.)
Completed hybrid Points creation

When Point fields or markers are indicated for removal, the draw
tool will be shown or hidden accordingly. Also, the button to add
new Point fields is disabled whenever the limit on the number of
Points has been reached. When a marker is deleted, its corresponding
disabled Point fields will also be removed.