Provide the client icon in the file browser context menu

[TheOneRing]

This feature was initially discussed in #6919 but as we provide branded clients just providing icon name is not possible for us.

• Provide a json based socket api call
• -> V2/GET_CLIENT_ICON:{"size": 256, "theme": "dark"}
• <- V2/CLIENT_ICON:{"size": 256, "theme":dark", "png": "blob" }
• https://github.com/owncloud/client/blob/master/src/gui/socketapi/socketapi.cpp#L838

The initial implementation should be used in https://github.com/owncloud/client/tree/master/shell_integration/dolphin

[TheOneRing]

Fixed in #8638

[jnweiger]

Confirmed fixed in testpilotcloud 2.9.0-beta3

• Provide a json based socket api call

• -> V2/GET_CLIENT_ICON:{"size": 256, "theme": "dark"}

• <- V2/CLIENT_ICON:{"size": 256, "theme":dark", "png": "blob" }

The exact syntax is:

• -> V2/GET_CLIENT_ICON:{ "id": "1", "arguments": { "size": 256 } }
• <- V2/GET_CLIENT_ICON_RESULT:{"arguments":{"png":"iVBORw0KGgoAAAA.... " }, "id": 1 }