Added Swarm iFrame for CORS support. Closes #6

Added in an activation hook to write out the swarmiframe.html file to
the root of the WordPress install. This file will be used to support
Cross Domain image and video hosting by way of an iFrame. Also cleaned
up code formatting.
Fixed 1x1 image src to use relative protocol. Fixes #5

Updated the image src of the 1x1 image to not specify the protocol so
that it will properly use http or https depending on the parent page.
Bumped version number to 0.1.5