Update ImageMagick dependency #10
Description
ImageMagick 6.7.7 (newest version available in Ubuntu 14.04 repos) has a deadlock when creating multiple images simultaneously from blobs in a threaded environment. There are a few candidate underlying bugs on their changelog, but in any case it's fixed in the current release, 6.9.1-4. Unfortunately this means compiling another dependency from source on all platforms and getting CMake to find it, so docs need to be updated.
Note this doesn't affect the normal process-distributed SOPNET, just the threads used for local development and inspection.
e: On 14.04 ImageMagick 6.9.1-10 is a core dumping mess that should be avoided. 6.9.1-4 should be preferred for now.