Until now the JOSE pieces only had enough support for ACME.
This patch improves the JWK parsing to prepare for more
complete support and for adding JWE, genaes and genec in
later patches.
1) update the logos to svg
2) add svg icon for strict security policy where used
3) define new vhost option flag to enforce sending CSP headers
with the result code
4) add vhost option flag to minimal examples to
enforce sending CSP where applicable
5) Go through all the affecting examples confirming they
still work
6) add LWS_RECOMMENDED_MIN_HEADER_SPACE constant (currently
2048) to clarify when we need a buffer to hold headers...
with CSP the headers have become potentially a lot
larger.
Firefox has a bug for 2 years
https://bugzilla.mozilla.org/show_bug.cgi?id=1262842
where a strict content-security-policy that is correctly followed
wrongly also defeats inline style inside SVG.
Apply the workaround told by the GIMP guys on the bug to convert
SVG styles to XML at export.
