[#61] Show error in inexistent routes

closes #61 (closed)

The error will be shown in the following cases:

• https://notifications.web.cern.ch/thispathdoesntexist
• https://notifications.web.cern.ch/channels/3ede6edf-7565-4308-b79b-c73e5859641f/channelexistsbutnotthispath