fix: suppress transient font family errors during signal propagation

[nyan-left]

Issue

Text components created before being connected to parent containers would log error unknown font family xxx, even though the font would become available once signals propagated.

Fix

Added a global font family registry to distinguish between transient states (font on way) and genuine errors (font doesn't exist).

[bbohlender]

@nyan-left Could you split up this into the fix and a new proposal

I would love to merge in the fix immediateliy, but the additional font families registriy increases the complexity of the repo which I am not a big fan of. I'd rather move that change to uikit 2.0 where a global font registry might be the only option instead of having 2 side by side.