Select script language in admin console

Please add a "language" parameter into admin console to switch between Lua, JS and other languages.

For example:
tarantool

localhost> print('Hello from Lua')
---
Hello from Lua
...

localhost> console.setopt('language', 'js')
localhost> console.log("Hello from JS")
Hello from JS
...

localhost> console.setopt('language', 'lua')
localhost> print('Hello from Lua')
---
Hello from Lua
...

Lua can be used as a default.

console.setopt(key, value) is proposed as an universal interface to set server-side options of admin console.
We (I with Kostja) decided during Skype discussion that the server also need server-side delimeter, e.g.
>console.setopt('delimeter', '\n')

Other options can be added in the future.