Refactor test of command to improve readibility

add a TYPE_INDEX = 1 in BlinkCommandTest

thanks @ludopradel for pairing with me on this one
use of SavePatternCommand to test instead of an anonymous ChangeColorCommand

as it is only usefull to check that parameter used to communicate with concrete usb device are ok, any command is find.
SavePatternCommand is a simple command, with no parameter. Better than ChangeColorCommand which is an abstract class.

Thanks @ludopradel for pairing with me on this one
Refactor BlinkCommand : type is set via constructor

add BlinkCommandType, an enum to describe type of command.
add BlinkCommand(BlinkCommandType type) : to set type of request via constructor
remove BlinkCommand() (constructor with no args)

thanks @ludopradel for pairing with me on this one
Merge pull request #8 from avernois/refactor_blink_command

Refactor blink command