so that we can change them for integration tests via the new ModularMailboxModule that now also includes the UrlProvider

one private message gets send via mailbox from one contact to the other

Upgrade obfs4proxy to 0.0.14-tor1 and enable uTLS for meek-lite

See merge request briar/briar!1730

Update meek bridge

See merge request briar/briar!1729

Use uTLS with Chrome profile for Snowflake

See merge request briar/briar!1728

Add TestLanTcpPluginFactory

See merge request briar/briar!1723

This factory provides a LanTcpPlugin that can connect to its own
address, useful for testing.

Use mailbox main branch for integration tests

See merge request briar/briar!1721

Fix imports for null-safety annotations

See merge request briar/briar!1720

End-to-end integration tests for communication via mailbox

Closes #2343

See merge request briar/briar!1699

Re-show mailbox unpaired dialog after screen-rotation

Closes #2358

See merge request briar/briar!1718

Don't re-add mailbox intro fragment after activity got destroyed

Closes #2367

See merge request briar/briar!1719

Use SOCKS socket library

See merge request briar/briar!1717

Use null safety library

See merge request briar/briar!1716

No longer crash when the Tor process crashes

Closes #2366

See merge request briar/briar!1715

Add Snowflake pluggable transport

See merge request briar/briar!1714

Added a separator to a sign out button

Closes #1074

See merge request briar/briar!1711