add feature to ignore buffers

[prauscher]

With the new setting "ignore" it is possible to specify a list of buffers which should be ignored on highlights. I use this for my bitlbee-buffers to avoid double notifications (twitter-app and #twitter_prauscher)

[prauscher]

Forgot to note: You need to specify the full name (like in buffer_autoclose, where i stole some code). This is $network.$buffer - e.g. Freenode.#spackeria