Add-on messages: add translator comments

[josephsl]

Hi,

Stemming from #73 discussion on messages:

One of the guidelines specified in NVDA community add-ons guide and review process is translator comments for messages to be translated. Perhaps due to the ad-don being developed prior to implementation of community-wide add-on review process, it might not had a chance to come with translator comments. Therefore go through add-on source code and add translator comments to messages to be translated by translators to make the life of translaotrs easier.

Thanks.