Add a "Waveforms" section

[cx1111]

PhysioNet is inextricably linked with waveforms. It hosts huge volumes of waveforms and lightwave. There should be a top-level page (physionet.org/waveforms) with:

• A brief intro/history of waveforms being hosted on PhysioNet
• A brief description of WFDB, and links to the official external WFDB sites.
• A list of databases that contain waveform files.
• A summary of waveform-related tools integrated into PhysioNet, such as LightWave and whatever may follow.

This section should be made configurable in the settings, given that other organizations are hosting their own instances of "PhysioNet".

[tompollard]

It would be good to use this as an opportunity/motivation to clean up the WFDB documentation, WFDB spec etc.