5.7.x replace current 7-Zip 32-bit with 64-bit version

[helptiger]

to switch fully to 64-bit pls replace also the 7-Zip 32-bit with the 64-bit version

[YasharF]

It looks like that the current bundled version of 7-Zip is v9.20. I didn't dig to see if the attack vectors apply to hMailserver's use or not, but there is an existing vulnerability disclosure for all versions of 7-Zip prior to v18.5: https://www.cisecurity.org/advisory/a-vulnerability-in-7-zip-could-allow-for-arbitrary-code-execution_2018-049
It would be great if 5.7 picks up the latest version of 7-zip.

[helptiger]

7-Zip v. 19.00 works great with hMailserver 5.7.x.

[YasharF]

PR: #305