Patch from Matej Laitl

* kmilo generic plugin is now configurable (no gui yet, one have to use kwriteconfig) - one can set which kmix channels to mute and set volume on (separately - needed for Intel HDA soundcards) and one can now fine-tune "slow" and "fast" volume steps (bugs 149183, 92730)
* when channels are not configured, query kmix for master channel
* some cleanups (removal of dupe code) and new volume computation algo changed
a bit (see comments is patch)
* unregister global shortcuts in destructor (bug 75169)
* support for controlling an extra channel, for people with surround sound
* README extended to contain relevant information