Resolve "Two-factor authentication"

Closes #2558

See merge request !1575

Resolve "Send email to reseller when quota is reached"

Closes #6346

See merge request ispconfig/ispconfig3!1608

Add Copy to clipboard button to shell user account and emailboxes

Closes #6230

See merge request ispconfig/ispconfig3!1543

Typo, update ispconfig.css

See merge request ispconfig/ispconfig3!1606

Avoid bashisms in the call to acme.sh

Closes #6326

See merge request !1595

This command is using features that are not POSIX-compliant (the [[ and
the || in them), that despite being supported by many shells (including
bash) are not available in dash.

Since system() runs the code with /bin/sh that is an interface defined
as only being POSIX-compliant, with no extensions, it should not presume
a specific shell in that.

Closes: #6326
Signed-off-by: Mattia Rizzolo <mattia@mapreri.org>

Resolve "Updated Italian translation (attached)"

Closes #6317

See merge request ispconfig/ispconfig3!1591

Changed 'Client Limit'-check and fixed styling

Closes #6320

See merge request ispconfig/ispconfig3!1593