Code cleanup + fixed small bug

Removed unneeded dummy slot;
Don't try to load project file while cancel is clicked
Added data in statusbar (closes #8)

Added indication "Running" or "Stopped"
Added communication success and fail count
Request iq only send when previous request has been handled (closes #7)

Removed poll time limitations
Show latest received value (closes #5)
Preparation for sliding window scaling of x-axis
Add sliding window scaling of X-axis (partially implements #12)
Fixed scaling modes (x and Y axis)