BrightEthereum: dynamically render mobile content

[Tomasvrba]

Currently, entering an Ethereum address generates a QR code with a deep link to BrightID verification. This is good for using the website on desktop and scanning the QR code with a mobile device, but the corresponding functionality is lacking to go to the deep link straight from a mobile device.

• [x] Mobile users should, instead of a QR code, see a button along the lines "Link to BrightID" which would open the deep link and route them to the BrightID App
• [x] For this, we need to dynamically render content based on UserAgent to distinguish between desktop/mobile/tablet devices

[Tomasvrba]

Implemented here: https://github.com/burnSignal/BrightID-EthereumAddressService/pull/14