Update proxy settings

[davidgoody-dfe]

Add new way of doing proxy settings that doesn't require writing your password into hard coded syntax

[adamrobinson361]

What do you think about this instead:

Sys.setenv(https_proxy = paste("http://ad\\",Sys.getenv("USERNAME"),":",
                               rstudioapi::askForPassword("AD account password"),
                               "@192.168.2.40:8080",sep=""))

We can make use of the USERNAME environment variable and then we only have to ask once.

[adamrobinson361]

Note if we are doing packagename:: we don't need library so either or works