Improve server-template description in advanced configuration (rebased onto develop) (rebased onto dev_5_0)



This is the same as gh-652 but rebased onto dev_5_0.

----



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

----

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