Update the Increasing JIRA Memory description and screenshots

The Increasing JIRA Memory guide that is available for JIRA 4.4.x is outdated and might be misleading. The URL is http://confluence.atlassian.com/display/JIRA044/Increasing+JIRA+Memory

Especially in the section:

As a rule of thumb, if you have fewer than 5000 issues, JIRA should run well with the default 256MB. Granting JIRA too much memory can impact performance negatively, so it's best to start with 256Mb and make modest increases as necessary. As another data point, 40,000 works well with 750MB.

In JIRA 4.4.x, it is run best with the default 758MB RAM for small instance.