added keyboard event handler to switch spectrogram mode.
added keyboard event handler to switch spectrogram mode.

joshblum/eeg-spectrogram,joshblum/eeg-toolkit,joshblum/eeg-toolkit,joshblum/eeg-spectrogram,joshblum/eeg-spectrogram,joshblum/eeg-toolkit,joshblum/eeg-spectrogram,joshblum/eeg-toolkit,joshblum/eeg-toolkit,joshblum/eeg-spectrogram