Closes #43. Add CommandRunner module to the app.

CommandRunner allows you to define a terminal command and arguments, run
it on a schedule, and view the output.

Examples:

   ping -3 cisco.com

cmdrunner/widget.go

@@ -2,6 +2,11 @@ package cmdrunner
 
 import (
 	"fmt"
+	"os/exec"
+	"strings"
+
+	"github.com/olebedev/config"
+	"github.com/senorprogrammer/wtf/wtf"
 )
 
 // Config is a pointer to the global config object
@@ -10,9 +15,42 @@ var Config *config.Config
 type Widget struct {
 	wtf.TextWidget
 
-	cmd string
+	args   []string
+	cmd    string
+	result string
 }
 
 func NewWidget() *Widget {
 
+	widget := Widget{
+		TextWidget: wtf.NewTextWidget(" 🏃 Runner ", "cmdrunner", true),
+
+		args: wtf.ToStrs(Config.UList("wtf.mods.cmdrunner.args")),
+		cmd:  Config.UString("wtf.mods.cmdrunner.cmd"),
+	}
+
+	return &widget
+}
+
+func (widget *Widget) Refresh() {
+	if widget.Disabled() {
+		return
+	}
+
+	widget.UpdateRefreshedAt()
+	widget.execute()
+	widget.View.Clear()
+	widget.View.SetTitle(fmt.Sprintf(" %s ", widget))
+
+	fmt.Fprintf(widget.View, "%s", widget.result)
+}
+
+func (widget *Widget) String() string {
+	args := strings.Join(widget.args, " ")
+	return fmt.Sprintf("%s %s", widget.cmd, args)
+}
+
+func (widget *Widget) execute() {
+	cmd := exec.Command(widget.cmd, widget.args...)
+	widget.result = wtf.ExecuteCommand(cmd)
 }