Allow bi-directional "rich data" (text, binary) clipboard

[brentpicasso]

Software Versions

• Python: 3.x
• OS: any
• Kivy: 2.3.0
• Kivy installation method: pip

Describe the bug The operating system's clipboard supports various types of data, in addition to text. Kivy's clipboard (kivy.core.clipboard) does not support anything but setting text values. Therefore, it is impossible to put binary data (e.g. images) onto the clipboard.

Proposed resolution: Fix the clipboard by allowing the supported object types

[misl6]

Agree, we should have bi-directional binary clipboard support.

Changing the title, and targeting it for 3.0.0.