Added dynamic memory management for shutters (functions in shutter.c).
Code is now much easier to tailor to specific needs and works better in the limited RAM of routers.
Memory leaks were not found by Valgrind Memcheck.
Reworked channel changing: now it tracks the current ch. and resets only once. This makes the program to finish faster.
Added rolltime_down and percentage values to shutter structure: now the schedule file needs to contain a percentage column after the timestamp for lowering, and a rolltime needs to be defined for each shutter in the beginning of the program. When lowering shutters, there's a calculation to sleep until the desired percentage is reached, when the shutter is stopped
The way to deactivate shutters has changed: now you need to set the percentage to 0.
