move getting mnemonic function from SeedVC to Identity

Session/Conversations/ConversationVC.swift

@@ -96,7 +96,7 @@ final class ConversationVC: BaseVC, SessionUtilRespondingViewController, Convers
         return margin <= ConversationVC.scrollToBottomMargin
     }
 
-    lazy var mnemonic: String = { ((try? SeedVC.mnemonic()) ?? "") }()
+    lazy var mnemonic: String = { ((try? Identity.mnemonic()) ?? "") }()
 
     // FIXME: Would be good to create a Swift-based cache and replace this
     lazy var mediaCache: NSCache<NSString, AnyObject> = {

Session/Settings/SeedModal.swift

@@ -10,7 +10,7 @@ final class SeedModal: Modal {
     // MARK: - Initialization
     
     init() throws {
-        self.mnemonic = try SeedVC.mnemonic()
+        self.mnemonic = try Identity.mnemonic()
         
         super.init(targetView: nil, dismissType: .recursive, afterClosed: nil)