Don't set a default port

[dominikl]

The connect method sets the default port to 4064 if no port is specified. That way you can't connect to websocket URL by simply...

server <- OMEROServer(host = "wss://localhost", username = "xx", password = "xx")
server <- connect(server)

...because the port will be set to 4064 by the R gateway. All the logic is already in the Java gateway, so this PR removes setting the default port in the R gateway, and above example should work.

See also #86

[jburel]

I am having a hard time building the docker image using the dockerfile under jupyter directory

library('romero.gateway')
Error in library("romero.gateway") : 
  there is no package called ‘romero.gateway’
Execution halted

[jburel]

using the other dockerfile

Error in library(devtools) : there is no package called ‘devtools’
Execution halted

[jburel]

I combined the changes in #88 and ran the adjusted notebook
I was able to connect with and without websocket

[jburel]

#88 should be merged first otherwise travis will fail