When putting app to background with qr scanner active, then moved to foreground again,
SimpleScannerActivity instance is not destroyed, but the local mScannerView was re-initialized
with a new instance (through startCamera()) regardless of pre-existing instance, and added to
the contentFrame. This leaves the previous mScannerView instance in limbo, potentially getting
garbage collected at unpredictable times.
Replaces the unmaintained and unreliable
`me.dm7.barcodescanner:zxing:1.9.8` qr code scanning library used only
on android with the `com.github.markusfisch:BarcodeScannerView:1.6.0`
(https://github.com/markusfisch/BarcodeScannerView) library which seems
more actively maintained.
The `BarcodeScannerView` library is incredibly fast and scanning qr
codes is now fun again :)
wip: still looking into ways to pin the library.
