For copy/paste support in our code samples, we are using the
ZeroClipboard library which relies heavily on Flash.
Because many browsers/extensions are disabling this plugin nowadays,
this commit replaces ZeroClipboard with a native, lightweight solution
for this feature.
When served with HTTP/2 and TLS, project pages show several mixed
content errors:
* the imported Google fonts
* the AJAX call to spring.io to get the current project information
* the newsletter iframe
This commit changes URLs to use https or protocol-relative URLs when
possible. This also deletes the now defunct newsletter integration.
