Improve server-template description in advanced configuration (rebased onto develop)



This is the same as gh-646 but rebased onto develop.

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Related to http://www.openmicroscopy.org/community/viewtopic.php?f=4&t=7400, this PR:

- uses the `seealso` markup in the Unix/Windows installation pages to increase visibility of the Advanced configuration
- reviews headings, code blocks and configuration files markup in the `Advanced configuration` page
- adds a paragraph about the JVM memory settings of individual server templates