Swapping of LED number assignation

LED objects correctly effect their corresponding LED. The initial error was
pretty harmless, though.
New files Button.{cpp,hpp}
FIX: Button::state now return the right state!

On the other file, only a line comment is added (just a visual thing).
New files Input.{hpp,cpp}.

They introduce Input and InputMan objects. They deal with buttons and allow
installation of handlers on events from buttons. Also removed code from
src/interrupts/stm32fxxx_it.c. Removed now obsolete function init_GPIO, and
commented-out EmergencyStop inclusion and use in main.cpp.

TODO: Doxygen comments...
Repurpose EmergencyStop

Now that inputMan handles all inputs and can call handlers on events,
EmergencyStop now provide a static method to install itself as an handler on
button::b3 pressed. Now, function initialize in main.cpp does exactly call
this static method.

TODO: Doxygen comments, with the respective authors.
Merge branch 'Button'

Doxygen comments are on the TODO list (as can be seen from Button branch
history), and will come eventually! Input and InputMan are usable.