Return runner's defer in Application.run

[touilleMan]

Hi,

I'm working on a lib to easily integrate autobahn in a synchronous application (see https://github.com/Scille/autobahn_sync)
Given I use crochet, the twisted reactor is already started when I run Autobahn.Application, which means I have to handle by myself the connection errors (see https://github.com/Scille/autobahn_sync/blob/53c7303a06cf53a783fabbc550b334d48d90d05a/autobahn_sync/core.py#L599)
This is fine except Autobahn.Application.run doesn't return the ApplicationRunner's defer.
To fix that I had to copy the Application.run function inside my app (see https://github.com/Scille/autobahn_sync/blob/master/autobahn_sync/core.py#L59), which feels like adding complexity for nothing...

[codecov-io]

Current coverage is 57.39%

Merging #603 into master will not affect coverage as of 757e1b4

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  Hit           5871    5871       
  Partial        556     556       
  Missed        3802    3802       

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[meejah]

LGTM, thanks:)