Improve UX for startup failures

Closes #1136

See merge request akwizgran/briar!706

Show a proper error message when database is too new or too old.

Inject StartupFailureActivity to prevent NPE

Closes #1176

See merge request akwizgran/briar!705

Improve QR code scanning on phones with high res cameras and slow CPUs

Closes #1068

See merge request akwizgran/briar!699

Use first byte of QR code payload for format version

Closes #1173

See merge request akwizgran/briar!702

Store Bluetooth address and UUID at first startup

Closes #1164

See merge request akwizgran/briar!694

Include requested messages when getting next send time

See merge request akwizgran/briar!704

Don't poll for retransmission

Closes #542

See merge request akwizgran/briar!695

Show an error fragment when an unsupported QR code is scanned

Closes #1134

See merge request akwizgran/briar!675

Add denormalised columns to statuses table

See merge request akwizgran/briar!691

Tap viewfinder to restart auto focus

Closes #509

See merge request akwizgran/briar!697

Don't poll disabled transport plugins

Closes #1137

See merge request akwizgran/briar!698

Use raw byte mode for QR codes

See merge request akwizgran/briar!696

Use a multiset for counting things

See merge request akwizgran/briar!688

Use Curve25519 for key agreement

Closes #236

See merge request akwizgran/briar!693

Use Ed25519 for signatures

See merge request akwizgran/briar!686

Note: Curve25519 is tested using standard ECDH and ECDHC over the Curve25519 curve.

Migrate schema when opening database

Closes #594

See merge request akwizgran/briar!680