Filtering predictions

[lopezjuanma96]

Similar to what other predictive keyboards do, if the user starts typing letters after getting a prediction, we can start filtering the predictions we have based on what the user is typing, so, if we got the predictions ["estomago", "casa", "pierna", "pieza"] and the user started typing "p", the first two would be filtered out (this includes not only the predictions that are shown, but also the ones that are listed for shuffling). Conected with #10, we should see if it's too complex to recover the filtered predictions when the user backspaces until it backspaces an empty space (that would have run the predicitons in the first place), when the whole list of predictions would be scrapped.