Made base class PlatformController to abstract out platform-specific
details such as default paths and how to start the scalyr agent as
a service in the background.  This is being done to support the
Windows port.

Updated all affect classes and removed the platform stuff out of
the Configuration class.
Fixed import ordering issue.
Merge pull request #1 from scalyr/czerwin-platform-refactoring

Refactoring of platform-specific code