REORG: include: move task.h to haproxy/task{,-t}.h

The TASK_IS_TASKLET() macro was moved to the proto file instead of the
type one. The proto part was a bit reordered to remove a number of ugly
forward declaration of static inline functions. About a tens of C and H
files had their dependency dropped since they were not using anything
from task.h.
diff --git a/include/types/server.h b/include/types/server.h
index a9d333e..a2f1fe3 100644
--- a/include/types/server.h
+++ b/include/types/server.h
@@ -40,7 +40,7 @@
 #include <haproxy/freq_ctr-t.h>
 #include <types/queue.h>
 #include <types/ssl_sock.h>
-#include <types/task.h>
+#include <haproxy/task-t.h>
 #include <types/checks.h>