When instantiating an account, set the default color to something

random, rather than blank, so that new accounts don't endup without
colors.

src/com/fsck/k9/Account.java

@@ -133,7 +133,7 @@ public class Account implements BaseAccount
         mExpungePolicy = EXPUNGE_IMMEDIATELY;
         mAutoExpandFolderName = "INBOX";
         mMaxPushFolders = 10;
-        mChipColor = 0;
+        mChipColor = (new Random()).nextInt(0xffffff) + 0xff000000;
         goToUnreadMessageSearch = false;
 
         searchableFolders = Searchable.ALL;