Save Plot doesn't seems to plot the entire recording

[aditydcp]

With the closing of issue #5, the app now allows recording beyond 30 seconds. However, saving plot beyond 30 seconds yields weird results. Possibly it doesn't save the entire recording, but only the first 30 seconds.
This might be due to how I didn't touch any of the code on EcgImager class.

But this is not the main priority, so no further action will be taken.