Textual now has a "Mute Sound" menu item inside of the File menu.

• Abstracted the mute toggling into IRCWorld.m, away from IRCClient.m where it doesn't appear to belong.
• "File -> ⇧⌘M Mute Sound" toggles mute
• Planning on added an a dictionary item for the defaults system for this setting.
Refuse to build if there's no CODE_SIGN_IDENTITY
Revert "Refuse to build if there's no CODE_SIGN_IDENTITY"

This reverts commit 4e09e0bbaaa498cc42091cdf836fd34259815626.
Revert "There, this should invert the swipe direction. I can't test it as I don't have a magic mouse. I'm sure milky will let me know."

This reverts commit 3013236bb640ead225b7e23d71f9440243667250
Merge branch 'master' of https://github.com/winny-/Textual into MuteToggle
Minor clean up of winny's code and save mute state to world dictionary. I don't like Mute Sound being under File... but I don't know where else to put it.