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/src/peers.c b/src/peers.c
index 3724346..e1a2525 100644
--- a/src/peers.c
+++ b/src/peers.c
@@ -25,6 +25,7 @@
 #include <haproxy/frontend.h>
 #include <haproxy/net_helper.h>
 #include <haproxy/obj_type-t.h>
+#include <haproxy/task.h>
 #include <haproxy/time.h>
 #include <haproxy/tools.h>
 #include <haproxy/thread.h>
@@ -45,7 +46,6 @@
 #include <proto/signal.h>
 #include <proto/stick_table.h>
 #include <proto/stream_interface.h>
-#include <proto/task.h>
 
 
 /*******************************/