Add rapidoc documentation. Set it as default.

[heyqbnk]

RapiDoc provides better displayed documentation. It looks way better than ReDoc and Swagger and its the reason, why it was used here. I have used colors which are closer to TON project to make it look more adapted, but most part of colors are dark not to burn out the eyes.

Here is how docs look now:

Additionally, set RapiDoc documentation as default. So, now, RapiDoc documentation is shown when visiting /api/v2/. Swagger docs were moved to /api/v2/swagger.

Added some comments and links in RapiDoc handler code about its customization.

[slavafomin]

Thank you for the work done.

I have used colors which are closer to TON project

The right color would be: #0088CC

Also, this looks weird ^

Can we fix it?