power_eeg_bands: Get power values for EEG bands
In adigherman/EEGSpectralAnalysis: Compute and plot various spectral EEG analyses

Calculate power values for each of the EEG bands: Delta < 4 Theta >=4 and < 8 Alpha >= 8 and < 14 Beta >= 14 and < 32 Gamma >= 32 and < 50

power_eeg_bands(
  eeg_signal,
  sampling_frequency = 125,
  max_frequency = 32,
  num_sec_w = 5,
  aggreg_level = 6
)

`eeg_signal`	EEG signal expressed in micro-Volts
`sampling_frequency`	Sampling frequency of the EEG signal. This is typically equal to 125Hz. Default value is 125.
`max_frequency`	The maximum frequency for which the spectrum is being calculated. Default value is 32.
`num_sec_w`	number of seconds in a time window used to obtain the Fourier coefficients. Typically, this number is 5
`aggreg_level`	number of 5 second intervals used to aggregate power. Typically, this number is 6 to ensure a 30 second interval window (standard in EEG analysis)