Fix a few -Wunused warnings
Cleanup
[yarpview-gtk] Add --keep-above argument
[yarpview-qt] Add --keep-above argument
Add YARP_INT32_FMT and YARP_INT64_FMT defines

These should be used when printing YARP_INT32 and YARP_INT64 variables
instead of %d, %ld, %lld to avoid warnings, for example:

   YARP_INT32 x = 32;
   YARP_INT64 y = 64;
   printf("x = %"YARP_INT32_FMT", y = %"YARP_INT64_FMT, x, y);
Fix -Wformat warning
Include diff_match_patch directory as "SYSTEM"

This option passes the -isystem option to the compiler that avoids
printing warning for these included directories.

We might want to do this for the other external libraries in the future.
Fix -Wunused warnings
Fix Wunused-variable warning
Fix Wunused warnings
[YARP_OS/Log] Check arguments of the c-style debug functions

This ensures that the arguments supplied have types appropriate to the
format string specified, and that the conversions specified in the
format string make sense. On gcc the warning is enabled by -Wformat.
[YARP_OS/Log] Improve reading of debug environment variables

Trace is now disabled when debug is disabled
[YARP_OS/Log] Simplify print_callback and forward_callback implementations

Hopefully it will not impact performances
[YARP_OS/Log] Use the full name for colored_output variable in color macros
[YARP_OS/Log] Remove extra space in final forwarded output line
[YARP_OS/Log] Use ACE_OS::snprintf instead of sprintf
[YARP_OS/Log] Fix -Wformat-security warnings
[YARP_OS/Log] Remove no longer used variables
[yarplogger] Make trace light grey instead of purple
[yarplogger] Initialize QApplication after ResourceFinder

On linux, QApplication "eats" the --name argument