Replace illustration for adding contacts nearby

briar-android/artwork/il_qr_code_dark.svg

briar-android/artwork/il_qr_code_light.svg

briar-android/artwork/il_qr_code_nearby_dark.svg

briar-android/artwork/il_qr_code_nearby_light.svg

briar-android/artwork/qr_code.svg

...oid/contact/add/nearby/AddNearbyContactIntroFragment.java

briar-android/src/main/res/drawable-night/il_qr_code.xml

...android/src/main/res/drawable-night/il_qr_code_nearby.xml

...droid/src/main/res/drawable-night/qr_code_explanation.xml

briar-android/src/main/res/drawable/border_explanation.xml

briar-android/src/main/res/drawable/il_qr_code.xml

briar-android/src/main/res/drawable/il_qr_code_nearby.xml

briar-android/src/main/res/drawable/qr_code_explanation.xml

briar-android/src/main/res/drawable/qr_code_intro.xml

...oid/src/main/res/layout-land/fragment_keyagreement_id.xml

...-android/src/main/res/layout/fragment_keyagreement_id.xml

briar-android/src/main/res/values-night/color.xml

briar-android/src/main/res/values/color.xml

briar-android/src/main/res/values/strings.xml