RFR: JMC-5541: Updating JMC landing page with new coordinates and screenshots

[Marcus Hirt]

Hi all,

Please review this fix to update the JMC update site landing page and
images.

Jira:  https://bugs.openjdk.java.net/browse/JMC-5541
Patch: http://cr.openjdk.java.net/~hirt/JMC-5541/webrev.0/

Kind regards,
Marcus