added keyboard shortcut navigation

added shortcuts are:
````javascript
+    var keyCodes = {    left:   37,     // navigate forward
+                        up:     38,     //
+                        right:  39,     // navigate back
+                        down:   40,     //
+                        one:   49,     // vote 1*
+                        two:   50,     // vote 2*
+                        three:   51,     // vote 3*
+                        four:   52,     // vote 4*
+                        five:   53,     // vote 5*
+                        num1:   97,     // vote 1*
+                        num2:   98,     // vote 2*
+                        num3:   99,     // vote 3*
+                        num4:   100,    // vote 4*
+                        num5:   101,    // vote 5*
+                        plus:   107,    // toggle image display size
+                        minus:   109,    // toggle image display size
+                        c:       67,     // focus cursor into comments field
+                        f:       70,     // toggle image display size
+                        h:    72,     // navigate to main page
+                        l:     76,     // login
+                        r:    82,     // load random image // TODO
+                        s:    83,     // focus cursor into search field
+                        u:    85      // navigate to upload form 
```