Docker cleanup and documentation

See merge request !29

More Docker changes

See merge request !28

* disable in-network updates
* persistent directory for snark downloads
* listen on port 12345 for i2np connections
* restore multi-stage build
* use better ant target
* allow passing -Xmx via the JVM_XMX variable

Many thanks to LoveIsGrief for the suggestions!

Only check for clients.config if there was no clients.config.d

Docker persistent home

See merge request !27

Remove old Main-Class from manifest
Add Class-Path to manifest

More test mods
Fix StringBuilderWriter.write(int)

Merged into my fork, not main repo

See merge request !26

(if you uncomment it)

Jetty server high CPU when client send data length > 17408

This affects SSL connections only, which is not part of our default setup.
Adapted from workaround at:
https://github.com/eclipse/jetty.project/security/advisories/GHSA-26vr-8j45-3r4w
Put the new checks directly in the unwrap() method,
rather than subclassing SslConnection, as that would require config file changes.

Patch to follow in next commit

Null-out the InputStream of the Buffer object when writing.  Fixes #17

Closes #17

See merge request !25

When checking whether to use Roaming appdata(like on older installs or on installs where people deliberately use Roaming appdata) also check whether clients.config exists and if it does, set home to Roaming appdata since people may be updating from routers before the migration to clients.config.d directories. This should fix #16

Add a unicode arrow to the buttons on the address book interstitial. More CSS tweaks to work on more resolutions

Fix CSS on redesigned address book interstitial page so it no longer overflows on narrow or short pages

TODO: set outbound addresses on transition to firewalled later

for local interfaces even when not force-firewalled, because REA2()
now needs them to set the IPs regardless

Make option buttons on addresshelper interstitial larger and contain their own descriptions. Place the button to proceed without adding on one side, place the button to save and continue on the other. Remove redundant save-and-continues.