[FIX] transaction without explicit remote

remote was instantiated as an object and checks through the class for `this.remote` would pass and cause 
unintended behavior

e.g. `.complete()` would view an undefined remote as untrusted and not allow local signing
e.g. calling `_computeFee()` with an undefined remote would crash ripple-lib
Merge pull request #191 from geertweening/fix/undefined_remote

[FIX] transaction without explicit remote