Update ui_strings.h

Initial Russian translation. Notes:
1. I am not sure how to translate "Tox ID" and if it must be translated at all.
2. I do not know what the 'nospam value' is. So I left it as "значение nospam" for now.
3.  I translated the "Call ringing" simply as "Звонок", since I cannot see such a message in my own client, so this variant seems reasonable.
Merge pull request #231 from v2e/patch-1

Update ui_strings.h