feat: add custom error view

[d-loose]

@anasereijo we can go over design and copy for all of those next week:

Error message when refreshing a single snap or switching the channel while it is running:

Generic error page with custom message for SnapdException(kind: 'network-timeout') (see #1479 and #1668)

Generic error page with custom message for SnapdException(message: 'too many requests') (see #1684)

Ref #1479, #1668, #1684

UDENG-3056 UDENG-3264