Add better customization in Preferences window

[alejandroautalan]

Add options to change font properties and icon sizes. Requested in alejandroautalan/pygubu#89

[alejandroautalan]

Note to self

This might require the following changes:

• Allow to add a NamedFont object in the designer
• Change designer font entry to specify a named font
• Modify font description saved in xml

[rolandhesz]

This would be awesome, on my PC pygubu-editor UI fonts are size 8 or 9 (the tooltip is a bit bigger, so that's helpful.)

[alejandroautalan]

Hello @rolandhesz, thanks for trying pygubu.

This would be awesome, on my PC pygubu-editor UI fonts are size 8 or 9 (the tooltip is a bit bigger, so that's helpful.)

Please tell me what OS you are using.

Regards Alejandro A.