SCRAM-SHA-1 support

SCRAM-SHA-1 support tested with ejabberd. Unfortunately, SCRAM
requires a lot (at least 4096) SHA1 computations. It is a bit too much
for JavaScript especially on slower machines and can result in browser
pausing for more than 100ms. Given above SCRAM support is disabled by
default, it can be enabled in JSJaCConfig or with connect method
parameter.