Get Sage ready for Linux distributions

by felixs for Sage Mathematical Software System

Sage is currently shipped as a software distribution that, next to genuine code, includes all dependencies as packages. Moreover, the core library and python modules cannot be compiled in a straightforward way, as most linux distributions expect. Aim of this project is to detach the build process of sage ("the software") from sage ("the distribution"). The goal is a build system that works within the context of Sage as well as for any gnu/linux distribution that ships the dependencies for Sage.