[BUG] Detect when port is in use

[mikaelkindborg]

When starting ETS 0.2.1 and having e.g. HyperReload already running on the same port, the following error message is shown. This should be handled by automatically choosing a different port or showing an error message.

Error: listen EADDRINUSE
    at errnoException (net.js:901:11)
    at Server._listen2 (net.js:1039:14)
    at listen (net.js:1061:10)
    at Server.listen (net.js:1127:5)
    at Object.CreateServerObject.self.start (/Users/eric/Documents/EvoThings/EvoThingsStudio_Mac_0.2.1/application/server/webserver.js:88:11)
    at startWebServer (/Users/eric/Documents/EvoThings/EvoThingsStudio_Mac_0.2.1/application/server/hyper-server.js:43:9)
    at Object.startServers (/Users/eric/Documents/EvoThings/EvoThingsStudio_Mac_0.2.1/application/server/hyper-server.js:271:2)
    at setupServer (file:///Users/eric/Documents/EvoThings/EvoThingsStudio_Mac_0.2.1/application/ui/hyper-ui.js:409:10)
    at file:///Users/eric/Documents/EvoThings/EvoThingsStudio_Mac_0.2.1/application/ui/hyper-ui.js:567:2
    at file:///Users/eric/Documents/EvoThings/EvoThingsStudio_Mac_0.2.1/application/ui/hyper-ui.js:568:3