Better error handling in the websockets support

[danieldk]

The alpinocorpus library has experimental websockets support (besides a more REST-like remote corpus reader). There is some error handling in that reader. Some things that are not dealt with currently, are:

• Interruption: what should we do if the connection is interrupted for a longer time and the websocket is closed? We should probably reopen it.
• There is currently no interface for error reporting to users (such as Dact), besides throwing exceptions. E.g. it is not possible for Dact to inform that the connection was closed, but attempts are being made to reconnect.

[danieldk]

I think the websocket support can be considered vaporware now ;).