Russian translation

src/main/res/values/arrays.xml

```
<?xml version="1.0" encoding="utf-8"?>
<resources>
    <string-array name="pref_theme_entries">
        <item>Светлая</item>
        <item>Тёмная</item>
        <item>Системная</item>
    </string-array>
    <string-array name="pref_theme_entry_values">
        <item>0</item>
        <item>1</item>
        <item>2</item>
    </string-array>
</resources>
```