Add the Russian ruble symbol to the list of currency symbols

**Describe the solution you'd like**
When you select "bbCodeWebex" / "Symbols" / "Currency" from the context menu, user can select the "₽" symbol, in addition to $, ¢, €, £, ¥, ₣, ₤, ¥CNY, ₨, ₹, ฿ and ₩.

**Additional context**
```
U+20BD
&#8381;
```