Fixed normal bug EXT-5831(Do not apply font color to timestamps in chat...

Fixed normal bug EXT-5831(Do not apply font color to timestamps in chat history) - added new 'ChatTimestampColor' color setting, which is set to timestamps for chat history messages in text mode which are not from log.
Reviewed by Vadim Savchuk at https://codereview.productengine.com/secondlife/r/160/.

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branch : product-engine