Dropping image onto canvas adds to local paper project (no server yet)
Added adding image to server (doesn't work yet)
Added default image position to center of canvas

Still not working on server - raised issue with PaperJS folks.
Fixed default image position
Fixed default image position on server
Fixed default image position on server for real
Fixed moving images on canvas
Added upload image button
Merge pull request #110 from tranek/develop

Added raster images