plugin: fix typo in temperature type
graph.php: fix undefined index 'type' in $plugin_json[$type]

When type wasn't set in the plugin json, a "PHP Notice:  Undefined index"
would pop up. Just default to 'default' when type isn't set.

Closes #76 #77
Add an 'ignore' graph type
New plugin: turbostat

(Edited from  Nicolas Iooss <nicolas.iooss_git@polytechnique.org>)
Keep the list of plugins sorted
Escape HTML in GET-provided hostname

A malicious user can enter javascript code in "h" GET parameter and this
code gets executed because this parameter is copied in the HTML output
without any escaping.  This patch escape the output before it is checked
it is valid.