Power library rewrite tracking issue

[alexisvl]

Placeholder: power library rewrite. The power symbol library has a large number of symbols that are identical except for their name, and as such should be generated by a script rather than handmade. This can ensure that a sufficiently comprehensive set of supply rails is created.

To be decided in this issue:

• Which voltages should be present?
• Which power symbol style should be used for each rail type?
• Ground symbols, in general. Which types should we have, and what should they be called?