UniversalBackForward: Convert side buttons to swipe gestures in Opera (…

…#483)

Opera's default actions for handling side buttons are not meeting our
expectations. Therefore, we should convert the side buttons to swipe
gestures when universal back and forward is enabled, in order to fix
this issue.

Closes #479.

LinearMouse/EventTransformer/UniversalBackForwardTransformer.swift

@@ -11,7 +11,8 @@ class UniversalBackForwardTransformer: EventTransformer {
     private static let includes = [
         "com.apple.*",
         "com.binarynights.ForkLift*",
-        "org.mozilla.firefox"
+        "org.mozilla.firefox",
+        "com.operasoftware.Opera"
     ]
 
     private let interestedButtons: Set<CGMouseButton>