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_stub.go

@@ -0,0 +1,71 @@
+// +build !darwin,!freebsd,!linux,!openbsd,!windows
+
+package gosigar
+
+import (
+	"runtime"
+)
+
+func (c *Cpu) Get() error {
+	return ErrNotImplemented{runtime.GOOS}
+}
+
+func (l *LoadAverage) Get() error {
+	return ErrNotImplemented{runtime.GOOS}
+}
+
+func (m *Mem) Get() error {
+	return ErrNotImplemented{runtime.GOOS}
+}
+
+func (s *Swap) Get() error {
+	return ErrNotImplemented{runtime.GOOS}
+}
+
+func (f *FDUsage) Get() error {
+	return ErrNotImplemented{runtime.GOOS}
+}
+
+func (p *ProcTime) Get(int) error {
+	return ErrNotImplemented{runtime.GOOS}
+}
+
+func (self *FileSystemUsage) Get(path string) error {
+	return ErrNotImplemented{runtime.GOOS}
+}
+
+func (self *CpuList) Get() error {
+	return ErrNotImplemented{runtime.GOOS}
+}
+
+func (p *ProcState) Get(int) error {
+	return ErrNotImplemented{runtime.GOOS}
+}
+
+func (p *ProcExe) Get(int) error {
+	return ErrNotImplemented{runtime.GOOS}
+}
+
+func (p *ProcMem) Get(int) error {
+	return ErrNotImplemented{runtime.GOOS}
+}
+
+func (p *ProcFDUsage) Get(int) error {
+	return ErrNotImplemented{runtime.GOOS}
+}
+
+func (p *ProcEnv) Get(int) error {
+	return ErrNotImplemented{runtime.GOOS}
+}
+
+func (p *ProcList) Get() error {
+	return ErrNotImplemented{runtime.GOOS}
+}
+
+func (p *ProcArgs) Get(int) error {
+	return ErrNotImplemented{runtime.GOOS}
+}
+
+func (self *Rusage) Get(int) error {
+	return ErrNotImplemented{runtime.GOOS}
+}