Add missing include files in .c files, add missing prototype in .h

Activate the warning for implicit functions in Makefile
Add the missing prototypes in .h
Add the missing #include in c files.
Fix function int GetWeeklySecondDifference(int weeklySeconds1, int weeklySeconds2)  unused parameter "day" is removed. Parameter "day" was not in the caller code.
-> All "implicit function" warning have been removed