Do not pass distance when requesting nearby trees

The server has a default value for distance. Removing this literal
parameter allows us to tweak the value on the server to produce the best
results without requiring a app update.
Fix nearby tree table cells

The table cells were expecting the OTM1 formatted JSON dictionaries and
were, therefore, displaying nulls for all items.

I temporarily disabled displaying the distance from the current location
to each tree because the unit of measurement needs to come from the
instance configuration, which is a larger feature that I don't want to
tackle right now.
Merge pull request #61 from azavea/topic/otm2-nearby-trees

OTM2 - show nearby trees