add a placeholder for MAEC content (until MAEC is supported)

[mattcoarr]

When MAEC content is encountered, add a placeholder warning so that the stix-to-html output doesn't break.

This is for 1.0 beta4. The next release will support MAEC, where issue #31 will be addressed.

Example content:

<ttp:Malware>
  <ttp:Malware_Instance xsi:type="maecInstance:MAEC4.0InstanceType">
  ...
  </ttp:Malware_Instance>
</ttp:Malware>

[mattcoarr]

fixed in 0cbd869a4f6d8b141e3823121f1ec79a45c04a63

may need additional changes if content aside from elements with xsi:type="maecInstance:MAEC4.0InstanceType" are to trigger the template text.

[johnwunder]

In STIX 1.1 w/ MAEC 4.1 the type will be MAEC4.1InstanceType, probably should have that trigger it too.

[mattcoarr]

For this MAEC placeholder template, now checks for MAEC 4.0 or 4.1

And it will check for any xsi:type in the MAEC 4.0 or 4.1 namespaces (previously it only looked for MAEC 4.0 MAEC4.0InstanceType instances):

• 'http://stix.mitre.org/extensions/Malware#MAEC4.0-1' OR
• 'http://stix.mitre.org/extensions/Malware#MAEC4.1-1'

These updates to check for MAEC 4.1 are in commit 895f1ef1a20cc8c6643737f0bf9f7931c310326f.