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

Remove unnecessary DB indexes

See merge request akwizgran/briar!687

Avoid queueing redundant DB tasks during sync

Closes #1162

See merge request akwizgran/briar!681

Prefer LAN addresses with longer prefixes

Closes #1148

See merge request akwizgran/briar!659

Don't show screen overlay dialog if all overlay apps have been allowed

Closes #1143

See merge request akwizgran/briar!658

Workaround for Samsung crash in Android 4.4

Closes #1116

See merge request akwizgran/briar!674