Volume icons in General tab of Preferences should be 'active'

Implemented on my part and awaiting decision from Evan. However, the following was raised in #adium: [11:07pm] <zacw> the slider in the sound preferences doesn't behave that way and it's the same as the adium preference

I guess we'll see if this lands at all.

Go ahead and attach your patch to the ticket in any case :)

I emailed it to you - do you want me to attach it here instead?

Patch added - aside from diff, a nib modification is needed - basically replacing the NSImageViews containing the icons with icon-only momentary change borderless NSButtons positioned and sized the same, and connecting to File's Owner (ESGeneralPreferences)' selectVolume: action.

Why 1000 for min and 2000 for max? The slider goes from 0.0 to 1.0 so far as I can tell.

It'd be better not to do a class comparison but instead hook the two new buttons - the minimum and maximum buttons - to IBOutlets in the nib file, then do a check against sender like:

if (sender == slider_volume) {
  volume = [slider_volume floatValue];
} else if (sender == button_minVolume) {
  volume = 0.0;
  [slider_volume setDoubleValue:0.0];
} else if (sender == button_maxVolume) {
  volume = 1.0;
  [slider_volume setDoubleValue:1.0];
}

Patch (diff and zipped nib with changes - turning volume icon NSImageViews to NSButtons) - try 2, now with less code and more outlets!

Good point. Changed patch accordingly.

(In [13042]) Patch from wootest, who writes: "When you click the respective 'quiet' and 'full' volume icons in the General tab of Preferences, the slider should snap to the level the icon indicates. iTunes does this, and the icons look big and clickable."

Closes #1088

It should be noted that this change requires changes in the nib. If there's a way to alert translators of this fact, it should probably be done.