Replacing startApp parameters with options object

- Replacing startApp parameters with object, because of too many arguments and also neat way of handling optional parameters.
- In anticipation of (Issue 2026) [https://github.com/appium/appium/issues/2026]
It's not critical, but you don't need this logic, you can use the startAppOptions  properties directly, just put some comment somewhere so that we know what options are expected.