Bug 1048845 - [Messages] Compose Panel refresh (subject behavior change). r=schung

I didn't have strong personal preferences about the property grouping. If the different type of properties won't get mix up, it would be fine for me then :) This strict rule is helpful for readability when we got bunch of properties in single styling, but it seems a little bit discrete for this case. Another minor concern is we don't do css minify currently, might be we will got very tiny overhead because of extra space, but I think we can ignore it anyway.