Add option allowing to reduce number of python copy/compilation targets

By globally defining the variable CTK_COMPILE_PYTHON_SCRIPTS_GLOBAL_TARGET_NAME to a
non-empty string or by specifying the macro option 'GLOBAL_TARGET',
the following targets will be defined for the whole build system:
 - Copy<GLOBAL_TARGET_NAME>PythonResourceFiles
 - Copy<GLOBAL_TARGET_NAME>PythonScriptFiles
 - Compile<GLOBAL_TARGET_NAME>PythonFiles

For complex projects, this can help reducing the number of targets and
simplify the manual rebuild of copy and compile targets.

Also make the custom command in charge of compiling the script dependent
of Copy${target}PythonScriptFiles target. That building a compile target
implies the associated copy target will be executed.
Compile python scripts explicitly instead of compiling an entire folder

Given the fact multiple compile targets can be associated with the same
destination directory, compiling each script explicitly will prevent two
compile targets build in parallel from compiling the same folder.
Regenerate python compile script at build time
Report a CMake error if script compilation fails
Merge branch 'option-to-reduce-compile-python-script-target-number'

* option-to-reduce-compile-python-script-target-number:
  Report a CMake error if script compilation fails
  Regenerate python compile script at build time
  Compile python scripts explicitly instead of compiling an entire folder
  Add option allowing to reduce number of python copy/compilation targets