Untangling interface and estimator code

Hi Paul,

I started to play with your filter. This pull request untangles the interface and estimator code. If you like the direction I could transform it into a C++ class, but I wanted to make small steps. In particular I have:

- Kept all variable names
- Kept the complete program flow
- Only split it into two files, so the log-loading main loop can be replaced by a different (e.g. live) main loop.
- Added a Makefile for simpler compilation

You can still compile on the command line using:
g++ -o estimator_closed_loop_test estimator.cpp main_closed_loop_float.cpp

Happy New Year!

-Lorenz