deleteMessage() and markMessageRead() should be able to accept an array of IDs

[airpingu]

Someone used to mention we've already fired a bug for this issue but I cannot find that so I open a new one. Please feel free to close it if duplicated.

In our current Mozilla implementation, we found eating an array of IDs can be very useful to improve the performance. Our experiments show it has to take around 30~40 seconds to delete 2000 messages if the delete method can only accept single ID. However, it can take just 5 seconds to delete all of them if the delete method can accept multiple IDs, because the back-end can simply open one DB transaction to finish the task from the point of view of implementation.

We might need to do the same thing for deleteConversation() and markConversationRead().

[zolkis]

+1
BTW, a previous version contained arrays, but someone complained in the first F2F, so we have removed it :).