[backport#12173] [Qt] Use flexible font size for QRCode image address
Summary:
Use flexible font size for QRCode image address (Jonas Schnelli)
Pull request description:
Bech32 addresses are currently cut off in the QRCode image in the GUI receive tab. This adds a simple font size calculation logic that "must" (down to 4pt) fix into the given image width. Examples OSX HiDPI: <img width="332" alt="bildschirmfoto 2018-01-12 um 11 25 40" src="https://user-images.githubusercontent.com/178464/34896144-c0c65d76-f78c-11e7-93e1-94dc8e203269.png"> <img width="322" alt="bildschirmfoto 2018-01-12 um 11 25 46" src="https://user-images.githubusercontent.com/178464/34896145-c0edfe1c-f78c-11e7-8c09-c15155e2160e.png"> Examples Ubuntu non HIDPI: <img width="314" alt="bildschirmfoto 2018-01-12 um 11 27 51" src="https://user-images.githubusercontent.com/178464/34896151-c88347f4-f78c-11e7-8a03-df8049dcfed6.png"> <img width="322" alt="bildschirmfoto 2018-01-12 um 11 27 42" src="https://user-images.githubusercontent.com/178464/34896152-c8bb881c-f78c-11e7-89d2-6f04ec608a19.png">
Backport of Core PR12173
Test Plan:
ninja bitcoin-qt -regtest, check the receive tab for correctness
Reviewers: #bitcoin_abc, deadalnix
Reviewed By: #bitcoin_abc, deadalnix
Differential Revision: https://reviews.bitcoinabc.org/D7524