Audio filter plugins

[essboyer]

Description

This PR adds a suite of audio filter plugins to the available audio pipeline plugins. The following new plugins are added:

• Highpass Filter
• Lowpass Filter
• Bandpass Filter

Highpass Filter

This is a classic highpass filter which implements the audiowsinclimit Gstreamer plugin.
The following controls are exposed to the user:

• Cutoff frequency (Hz)
• Window Mode

Lowpass Filter

This is a classic lowpass filter which implements the audiowsinclimit Gstreamer plugin.
The following controls are exposed to the user:

• Cutoff frequency (Hz)
• Window Mode

Bandpass Filter

This is a variable bandpass/band-reject filter which implements the audiowsincband Gstreamer plugin.
The following controls are exposed to the user:

• Lower cutoff frequency
• Upper cutoff frequency
• Filter mode (Bandpass/Band-reject)
• Window Mode