Various issues and improvements in y[n] tab

[chipmuenk]

Bugs

• Zoom lock doesn't work with spectrogram or when plot styles are modified
• Spectrogram for fs = 0 ... 1 or -0.5 ... 0.5 doesn't display correctly
• Check spectrogram scaling

Improvements

• Add stimulus type sinc
• Implement padding for spectrogram with N_overlap > 0 with options 'none' / 'circular' / 'zeros' / 'copy'
• Implement zero padding for smoother frequency plots
• Use a periodogram for long simulations
• fast plotting library optimized for large data sets like vispy
• Implement a slider for long simulation plots combined with fast replot