Fix Photo Upload for OTM2 API

* Sign POST requests with byte bodies
* Basic store of photo reponse object on tree, no display
Auto-format
Fix add tree photo for new plot

Handles local empty plot objects.
Photo only uploads on save

Previously, when editing the plot, the photo would be uploaded
immediatly, making "cancel" not actually work and a bad UI.
Now edit works like add, meaning a photo is only uploaded after
a successful plot save.  Better UI and removes a lot of
conditionals
Merge pull request #32 from OpenTreeMap/topic/upload-tree-photo

Upload tree photos