Keeweb: Support KDBX4 and Argon2

[antelle]

KeePass will have Argon2 password derivation function soon, instead of AES-based one. As WebCrypto doesn't provide built-in Argon2, we have to build it using asm.js and switch to WebAssembly, once it's supported.
Reference implementation, CC0:
https://github.com/P-H-C/phc-winner-argon2
Blake2 in js, CC0:
https://github.com/dchest/blake2s-js
https://github.com/dcposch/blakejs
libsodium (ISC license, C++ lib):
https://github.com/jedisct1/libsodium
libsodium in asm.js (ISC license, huge size ~800kb):
https://github.com/jedisct1/libsodium.js
KeePass thread:
https://sourceforge.net/p/keepass/discussion/329220/thread/a48066c0/
.NET implementation (some ideas for vector optimizations there; MIT license):
https://github.com/kmaragon/Konscious.Security.Cryptography
KDBX4:
http://keepass.info/help/kb/kdbx_4.html
Bad news here is that most probably we'll be a lot slower than desktop app.

[antelle]

First sketch of Argon2: https://github.com/antelle/argon2-browser#argon2-in-browser

[antelle]

First preview deployed to beta.keeweb.info

[antelle]

release published