dashboard: CPU, memory, diskIO and traffic on the footer (#15950)

* dashboard: footer, deep state update

* dashboard: resolve asset path

* dashboard: prevent state update on every reconnection

* dashboard: fix linter issue

* dashboard, cmd: minor UI fix, include commit hash

* dashboard: gitCommit renamed to commit

* dashboard: move the geth version to the right, make commit optional

* dashboard: memory, traffic and CPU on footer

* dashboard: fix merge

* dashboard: CPU, diskIO on footer

* dashboard: rename variables, use group declaration

* dashboard: docs

vendor/github.com/elastic/gosigar/sigar_util.go

@@ -0,0 +1,22 @@
+// Copyright (c) 2012 VMware, Inc.
+
+package gosigar
+
+import (
+	"unsafe"
+)
+
+func bytePtrToString(ptr *int8) string {
+	bytes := (*[10000]byte)(unsafe.Pointer(ptr))
+
+	n := 0
+	for bytes[n] != 0 {
+		n++
+	}
+
+	return string(bytes[0:n])
+}
+
+func chop(buf []byte) []byte {
+	return buf[0 : len(buf)-1]
+}