Replaced variable names options/inputs with fields/types.

Why I decided on options/inputs in the first place is now beyond me. It might
have something to do with dynamically created <option>s and <input>s I guess.
Removed group argument from query to _view/types-fields.

It makes no sense, but the group_level argument is ignored when combined with
&group=true and the view employs exact group level instead. It still works as
expected but with way more rows than needed.
Switched to jQuery.getJSON(url, data, success) in map.html.

In this one case it is a visual improvement. In any other case, I find the
inline object to make the source line a bit too long.
Rephrased explanation in script/require.js.
Simplified change()-handlers in upload.html.

On the downside the nice and helpful tooltip is now gone, but this thing was a
nightmare for internationalization anyway. Closures have been removed using the
data member of the event object. JSON.parsed values are explicitely converted
to strings, because $.val() handles null/undefined differently.
Applied relay_geometry() to feature list.

In summary, this checks if a document's geometry is used by other documents and
is about to be changed:
- in case the document will be deleted by the next bulk upload, its geometry is
  moved into one of the affected documents,
- in case the document's geometry is replaced by a geometry clone, all affected
  documents receive the same clone,
- and nothing happens in case the document's geometry is changed (meh).
Changed filter-remove-buttons to initialize only once.
Hid #type-is filter item on empty input.
Fixed missing <_id equals> filter item.

The fields first character is an underscore, so it is mistaken for _keyword or
_expression where no field name is required. Still, if the value is empty, no
filter will be applied (sweet).