Filter $versions values before print them on footer

[rdwebdesign]

What does this PR aim to accomplish?

Fix #2367.
This assures no unwanted scripts could be passed to the browser, to avoid arbitrary code is injection.

How does this PR accomplish the above?

Allowing only a minimum set of characters for version/branch/commit values.
(Upper and lowercase letters, digits, dot, colon, dash, underscore and slash).

We decided to allow any strings on the file and encode the output before printing on HTML page.

What documentation changes (if any) are needed to support this PR?

none

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[yubiuser]

Can we get this on a line-by-line approach and print "N/A" for lines that are affected? Also if the left-hand side of e.g. "WEB_BRANCH=mast§$$§er" is affected the current implementation will print vDev which seems not right.

[xPaw]

It's better to just use something like htmlspecialchars when printing, instead of trying to filter the string.

[yubiuser]

Before:

After: