Message of the Day functionality

[gninja]

Here's a patch to add MoTD functionality.

The message is displayed on the console index for non-guest users. And in the graph header for guest users. It's set through the settings page.

Patched against 0.8.6b, no testing has been done for other versions.

To install, untar in your cacti directory, then apply the three diffs.

[gninja]

Checked it with 0.8.6c, works fine.