Move source

[BlackEdder]

This moves the scid dir to source/scid.

I als updated all three of the build systems (dub, build.d and Makefile) and tested them as well as I could, i.e. I tested the following commands

dub
dub test
rdmd build
rdmd build lib
rdmd build headers
rdmd build html
make

[kyllingstad]

Awesome, thanks!