Include firewall configuration into JIRA DC docs

Please improve Installing+JIRA+Data+Center documentation page.
Suggested changes:

• Include section about ports used by JIRA DC, see as a example: https://answers.atlassian.com/questions/42692523/what-is-the-random-port-opened-by-jira-datacenter-used-for-and-what-is-the-range-of-choices
  • Main idea: JDC in addition to usual ports used by JIRA used 2 more ports for Ehcache: 40001 and 40011 (TCP ephemeral port)
• Include firewall recommendation, partially done in Security section
  • Until feature request JRA-64974 is implemented, large range of ports needs to be open (depends on OS, see TCP ephemeral port).
  • In JIRA 7.3 specific ports can be used