Timeout errors are not visible to the user

[dennwc]

Steps to reproduce:

1. Go to http://play.bblf.sh
2. Change language to "JavaScript"
3. Paste a large file (example)
4. Click "Parse"

What happens

Nothing. there is still an old UAST in the right panel and no indication of failed parse request.

What is expected

Looking at the console, there is clearly a timeout for parse request. It should be displayed to the user with a suggestion to try a smaller file.

[smacker]

it was partly fixed on master. Now it shows "internal error":

[dpordomingo]

@smacker I think we should try to show that it was a timeout error, shouldn't we?
And even better if the dashboard can also say in which part of the communication did it happened

[smacker]

that's why I said "partially".

[smacker]

Current bblfshd and client-go don't have default timeouts anymore. We don't add any timeout too.
So this bug isn't reproducable locally anymore.

In a hosted enviroment proxy can timeout and this error is displayed correctly (I saw it but I can't reproduce it anymore for a screenshot, bblfshd became too fast).

So here is nothing to fix.

But I added correct handling of request cancelation & correct http error in case bblfsh will add some timeout in the future.