- install package 'vim-common' to have 'xxd' needed by the compilation
  process of the T tracer
- change the way xxd is called so that no file is created in case
  of error

plus some cleanup here and there

The T only works when it's TRUE, the version without shared memory
is not supported anymore.

as special events.

If we store all received events to a file, this dump is now
self-contained. Helps to analyze traces.

Some functions have also been factorized in the process, too much
duplication.

(Also tracer/Makefile was forgotten in previous commit, included
in this one...)

only works for 5MHz (7680 samples per TTI), one transport block
(basic FDD thing)