Skins: add loop cue icons

[ronso0]

LateNight classic
Not ideal but there'a clear distinction between hotcues and loop cues.

Deere

Tango

Since bg icons are scaled (down) it looks non-ideal in samplers and squeezed decks, but better than nothing

Re squeezed decks: I'll open a PR to increase Tango's minimum size. With most configurations it'll still fit into 1024px screens but at least we don't get complaints it looks bad when we still claim to support 1024px.

Shade
I ave no patience to fiddle with the PNGs, I just added a WIP GiMP template.
If someone wants to finish that:

• move hotcue icons from <State> nodes in xml to style sheets
  WHotCueButton[displayValue="0"] for empty state
  WHotCueButton[displayValue="1"], WHotCueButton[displayValue="2"] for loaded and 'active' state, add hotcue icons per hotcue number
• add WHotCueButton[displayValue="1"][type="loop], WHotCueButton[displayValue="2"][type="loop] selectors, add loop cue icons per hotcue number

[daschuer]

LGTM and works good. Thank you.
I will take a look at Shade.