Convert to a "1.5 style library"

This moves all source into src/ and adds a library.properties file.
Note that this does not really restructure the source yet, there is
still a "src/utility" folder that should be removed next.
Fix include in Backpack.cpp

Now that "utility" is no longer a special folder, it does not appear in
the include path when compiling the library. Thus using
`#include <Backpack.h>` now failed.
Remove js0n code, use an external library instead
Remove Bootstrap example

This sketch also lives in the firmware-pinoccio repository, so this
prevents maintaining duplicate code,
Shuffle all code around

This removes the old utility directory and moves a lot of code from that
directory as well as the root src directory into subdirectories. This
should make the code structure a bit more clear.

This only moves code and updates include paths, nothing is actually changed.