AudioInput: spell out "Echo Cancellation" in the Audio Input config dialog

[mkrautz]

Right now, at least in English, it simply says "Echo".

That is very misleading, and does not make sense to many people, unless they know the setting has to do with echo cancellation in the first place.

We should rename the label echo cancellation. (It might not fit with the current layout, we will have to find a solution).

We should perhaps also rename the values of the combo box to explicitly mention echo cancellation ("Mixed echo cancellation", "Multichannel echo cancellation").

[mkrautz]

Fixed by #1942