Fix failure to enable fields after "add another tree"

The marker was being recreated but its 'dragend' handler wasn't being reset.
Solution is to only create the marker once, and only enable its dragend handler once.
That also allows simplifying the code by removing bindMarkerEventsOnce().

Also:
* Unbind popup when leaving browseTreesMode so it won't reappear
* Patch Leaflet so it won't crash
Simplify plotMarker.js

`addMarkerToMap`:
* Rename as `onMarkerPlacedByClick`
* Don't export, as it's not referenced externally
* DRY it out by calling onMarkerMoved(), which does exactly what the removed lines do

Also:
* Remove markerPlacedByClickBus (and its exported name markerPlacedByClickStream) are currently unused (`markerPlacedByClickStream` was referenced in addTreeMode.js, but so is `markerFirstMoveStream` and that will
have an event whenever the other would have.)
Use OTM2 favicon.png instead of Azavea favicon.ico

Our target browsers should all support using a .png
Merge pull request #777 from RickMohr/fix-add-another-tree

Fix "Add another tree"
Fix template typo: isntance -> instance

fixes #775 on github.

The 'Move Tree' button data-always-enable attribute was always being set to "False" because of this typo, causing the button to remain disabled by the buttonEnabler.
Merge pull request #783 from steventlamb/bug/775/disabled_move_tree

Fix template typo: isntance -> instance
Hide readonly field on plot_detail

fixes #772 on github.
Provide an interface for creating instances in ui tests

The regular site can simply call 'make_instance', however, if addons are
installed the restrict or change how instance creation is done it breaks
the workflow.

The solution used here is to override the instance creation in settings.py.
Add in basic map tests for adding trees
Merge pull request #784 from steventlamb/bug/772/hide_readonly_field

Hide readonly field on plot_detail
Work around IE9 console.error not being bindable

Since console functions do not inherit from Function, underscore cannot
bind them, since it thinks they are plain objects...
Use JSONP on IE9 for UtfGrid requests, since IE9 doesn't support CORS

fixes #746, fixes #747
Fix settings.py TILE_HOST documentation to be accurate
Merge pull request #785 from ahinz/topic/add-on-map-page-selenium-tests

Topic/add on map page selenium tests
lint
Refactor create instance function
Add in tests 'add another with ___' options
Merge pull request #788 from ahinz/topic/more-add-page-test

Topic/more add page test
Merge pull request #781 from RickMohr/otm2-favicon

Use OTM2 favicon.png instead of Azavea favicon.ico
Merge pull request #786 from maurizi/topic/ieFixes

IE9 fixes