[LyX/master] Update ru.po and UserGuide

[Yuriy Skalko]

>> If previous versions will be left, then there will be duplicated items in
>> menu since these linguistics tables "tableaux" translate just as "tables".
>> So I added these "(ling.)" prefixes to distinguish them.
>> 
>> There is also a calque from "tableau" word, but it has different meaning and
>> does not fit here.
> 
> 
> Well I doubt that you want to have "Table (lit.)" in the latex output, but if
> there is no corresponding word for tableaux in your language, then this whole
> discussion is probably void anyway.
> 
> In next iteration I'll replace the strings in layouttranslation in whatever
> you decide is best and is present in the .po file.
> 
> Pavel

So, in several linguistics articles I've found another term used for 
tableau -- матрица/matrix instead of таблица/table. Let's hope linguists 
will be happy with this or will reply and come up with better translation :)

Yuriy