UI: set rjr headers stored server side on session creation

These need to be set before the call to users::login occurs
to that the server can properly store the client rjr endpoint
for security
UI: add helpers to js ship/station to set system (and use them)
Replace system(middleman) w/ exec(middleman) calls in Rakefile

Since Rakefile process doesn't need to be kept around after
middleman is launched, we can replace the entire process
w/ exec instead of launching a shell based subprocess
w/ system (for more concise signal / process handing, etc)

Calls to middleman should be replaced with their full paths
for security in the future