1. - Added calls and parameters for Ewald periodic gravity (although not Ewald class yet)
2. - Changed boundary types to enum for performance with Ewald
3. - Added brute-force periodic SPH gravity
Added SPHTree routine for periodic gravity (not working yet)
Combined working Ewald class with new ICs for testing Ewald gravity
Merge branch 'master' of https://github.com/gandalfcode/gandalf
Added Ewald class