Move GTK specific code from core cpu-x.c to file gui_gtk.c
Clarify code on conditionnal compilation when possible
See this for reference: https://www.gnu.org/prep/standards/html_node/Conditional-Compilation.html#Conditional-Compilation
Fix wrong array initialization
Initialize strings in NCurses mode
Rename variable to fix compilator warning
Parsing options with getopts_long()