Make SNAKE translatable

This PR contains the following changes: 
- making all string variables translatable;
- usage the custom keybinding instead of hardcoded one;
- astyling of files iuse_software_snake.cpp/.h;
- bonus: game over screen (see screenshot below).

![game_over](https://f.cloud.github.com/assets/5421954/2238534/54d4b812-9bf4-11e3-9e55-c3500ec25e5b.png)


Hint: use a handheld game system for testing this PR.