Having a building system

As the repository of Gatekeeper grows, the need for a build system is growing as well. Right now, Gatekeeper has a makefile derived from DPDK that doesn't account for individual file changes (i.e. it requires `make clean; make` to compile after a single file change), side applications (e.g. `generate_if_map.c` and `gkctl`) do not have makefiles, and our makefile doesn't have an install target; this latter issue is currently mitigated with the Debian packages.

This issue should be solved in phases to avoid disrupting the development. The following is a general suggestion for the steps to follow:
1. Fixing the bug in the makefile that makes it ignore dependencies during incremental compilation;
2. Adding makefiles to side applications;
3. Adding an install target and adjust the Debian packages to use it;
4. Identifying **immediate** building problems that should be addressed at this point;
5. Adopting a build system.

DPDK uses [the meson build system](https://mesonbuild.com/), but one should look for alternatives before committing to a build system.