Return false if instanceuser is None

fixes

"""
ERROR: test_plot_detail (treemap.tests.urls.TreemapUrlTests)

[localhost] out:   File "/usr/local/otm/app/opentreemap/treemap/templatetags/instance_config.py", line 50, in is_deletable
[localhost] out:     return obj.user_can_delete(instanceuser.user)
[localhost] out: AttributeError: 'NoneType' object has no attribute 'user'
"""
Fix localization of tree ids

This was causing malformed urls on servers with >1000 trees, due to the presence of commas.
Use values() instead of objects in _load_itree_code_overrides()
Management command random_trees now takes an option for probability of diameter existing
Require species (rather than otm code) for benefits calculation

Now that we have ITreeCodeOverride's, species without OTM codes can contribute to benefits calculations