#2430 Revised adaptor icons and naming

[StephanZiegler]

Following @tobolar's suggestions in:

1. Icons:

• removed shading in icons for improved clearity in partial adaptor
• added colored rounded rectangle in domain specific adaptors
• unified sizing and location of real input icons

2. Naming:

• renamed XToYAdaptor to GeneralXToYAdaptor

close #2430

[tobolar]

I guess the original icon of Modelica.Mechanics.Rotational.Components.AngleToTorqueAdaptor (and TorqueToAngleAdaptor) was fine since it really concerns particular components in Rotational library - in contrast to general adaptors. So grey shaded rectangle icon should be reused to be able to simply distinguish between that "flat" adaptor and the general one.
I would open new PR.