Add a date and datetime meter (#159)

Add a date meter and sort header and source files in Makefile

Change the lists of header and source files sorted alphabetical and one
file per line. This way diffs become better readable and merges easier.

dragonflybsd/Platform.c

@@ -15,6 +15,8 @@ in the source distribution for its full text.
 #include "LoadAverageMeter.h"
 #include "UptimeMeter.h"
 #include "ClockMeter.h"
+#include "DateMeter.h"
+#include "DateTimeMeter.h"
 #include "HostnameMeter.h"
 #include "DragonFlyBSDProcess.h"
 #include "DragonFlyBSDProcessList.h"
@@ -78,6 +80,8 @@ void Platform_setBindings(Htop_Action* keys) {
 MeterClass* Platform_meterTypes[] = {
    &CPUMeter_class,
    &ClockMeter_class,
+   &DateMeter_class,
+   &DateTimeMeter_class,
    &LoadAverageMeter_class,
    &LoadMeter_class,
    &MemoryMeter_class,