Added QR scanner to wallet send card

[patrickbunetic]

PR Checklist

Please check all that apply to this PR using "x":

• [x] I have checked that this PR is not a duplicate of an existing PR (open, closed or merged)
• [ ] I have checked that this PR does not introduce a breaking change
• [ ] This PR introduces breaking changes and I have provided a detailed explanation below

PR Type

What kind of change does this PR introduce?

• [ ] Bugfix
• [x] Feature
• [ ] Code style update (formatting)
• [ ] Refactoring (no functional changes)
• [ ] Documentation changes
• [ ] Other - Please describe:

Fixes

Issue Number: #202

What is the current behavior?

There is no QR scanner for sending funds to an address encoded as a QR code.

What is the new behavior?

In the Wallet's Send card, there is now QR scanning functionality which will fill the recipient address with the value the scanner gets.

Other information

The QR library (zxing 4.1.0) works on SDK 24 and up, but I added a 'fallback' for 3.3.0 as they advise so the minimum SDK of 21 should still work and be able to use the functionality. I was not, however, able to test this on any devices with that SDK version.

[tzarebczan]

Thanks so much for the PR! We'll get another closer review on it soon.

Can we show you some appreciation?