point Safe Browsing link on settings page to site-specific URL

[stklcode]

We already generate such link in the warning mail, so why not show it on the settings page, too.

mentioned in #104

[Zodiac1978]

LGTM and works as expected.

The only idea I have is to add target="_blank" to the link and rel="noopener noreferrer" but I don't have a strong opinion on that.

[stklcode]

Me neither, but we do open all other links (donation, documentation, support) in a new window, and thus it seems legit to do the same here.

[codecov-commenter]

Codecov Report

Merging #106 (dae30c2) into develop (b9c9afd) will decrease coverage by 0.43%.
The diff coverage is 0.00%.

@@              Coverage Diff              @@
##             develop     #106      +/-   ##
=============================================
- Coverage      39.43%   39.00%   -0.44%     
  Complexity       143      143              
=============================================
  Files              5        5              
  Lines            535      541       +6     
=============================================
  Hits             211      211              
- Misses           324      330       +6     

Impacted Files	Coverage Δ	Complexity Δ
antivirus.php	0.00% <ø> (ø)	0.00 <0.00> (ø)
inc/class-antivirus.php	21.76% <0.00%> (-0.42%)	83.00 <0.00> (ø)

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