replace the "Unknown influence" glyph by the "Influence" glyph

[adrienrougny]

To be consistent with PD, the "Unknown influence" glyph could be replaced by an "Influence" glyph (PD counterpart: "Modulation" glyph), with the following less restrictive definition, adapted from PD: "A general influence where the exact nature of the influence is not specified or not known."

[tczauderna]

I think, it's a breaking change. Thus, I would rather prefer to make this change in a major update.

[rupertoverall]

Is the new definition a breaking change? It is less restrictive so should be backward-compatible.
I also prefer the new name and we could maybe change this while keeping the (deprecated) old variant.