[modules] Add initial version of a load module

Add a load module that shows 1/5/15 minute load average and allows the
user to set warning and critical thresholds on the 1 minute average.

fixes #9

themes/default.json

@@ -17,6 +17,9 @@
 	"cpu": {
 		"prefix": " cpu "
 	},
+	"load": {
+		"prefix": " load "
+	},
 	"disk": {
 		"prefix": " hdd "
 	},

themes/gruvbox-powerline.json

@@ -33,6 +33,9 @@
 	"cpu": {
 		"prefix": "  "
 	},
+	"load": {
+		"prefix": "  "
+	},
 	"disk": {
 		"prefix": "  "
 	},

themes/powerline.json

@@ -32,6 +32,9 @@
 	"cpu": {
 		"prefix": "  "
 	},
+	"load": {
+		"prefix": "  "
+	},
 	"disk": {
 		"prefix": "  "
 	},

themes/solarized-powerline.json

@@ -33,6 +33,9 @@
 	"cpu": {
 		"prefix": "  "
 	},
+	"load": {
+		"prefix": "  "
+	},
 	"disk": {
 		"prefix": "  "
 	},

themes/solarized.json

@@ -32,6 +32,9 @@
 	"cpu": {
 		"prefix": " cpu "
 	},
+	"load": {
+		"prefix": " load "
+	},
 	"disk": {
 		"prefix": " hdd "
 	},