Packed the `Panel' `x' and `y' position value into a `point_T' object.
Create a margin_T type to bundle the margin values.
Replaced `Panel.nb_desktop' to `Panel.desktop_count' and changed its type to
uint8_t.
Did some minor changes such as:
  => Replaced the type `Color' to a new one `color_T' which is also a 32bit
     color but easier to use less uggly interface and less error prone. This
     new type is introduced in the files src/util/color.{c,h}.

  => Removed all unreachable code.

  => Fixed all warning messages, and now in development mode everything is compiled
     with -Wextra, -Werror and some other warning flags.

  => Improved the function `src/common.c:copy_file(char*, char*)', which was leaking
     a file handler in case an error occurred during the opening the destination file.

  => Removed src/tintoconf.

  => Replaced all raw printfs to a debug macro defined in src/util/debug.h acording
     to the context.