- when we arrive to a point when all input params are empty, disable the
middle Exchange button
- add QML test for the Exchange button enabled/disabled state
Fixes#15751
- new panel created: `SwapInputPanel`
- some cleanups to the needed stores
- created a SB page demonstrating the use of 2 panels and the
`SwapExchangeButton`
- created QML tests
Fixes#14781
- create a custom circle button component for the Swap popup, with the
needed click event and a border area that can be overlaped with the
background as it looks in the design
Fixes#14782
Lukáš Tinkl