Internet Gateway enhancements and tweaks

- Tweaked "toInternetGateway" to be capabable of handling both list and
get Ref #717
- Added ability to list internet gateways Close #418
Add new method to delete Internet gateway by Id

Close #734
Add method to support looking up subnet by id rather than network id

Close #738
changes to get a single autoscaling policy by id

Ref #743
replace index 0 with index 1 and return statement

Ref #743
Merge pull request #20 from TheWeatherCompany/twc_dev

Twc dev