12311 auto memory

See: http://trac.openmicroscopy.org.uk/ome/ticket/12311

This PR removes the need to use perl or sed to modify the configuration properties on deploy. In fact, all references to `-Xmx` and `MaxPermGen` have been removed from `templates.xml`. Instead, the `omero.install.memory` module now calculates the appropriate settings **on every startup** and sets them in `config.xml`.

Things to check:
 * `bin/omero admin memory` command should modify `config.xml` and print out what it's doing
 * `bin/omero config set` can be used to modify those values
 * `bin/omero admin start` should make use of those properties.

Items that could use work/discussion:
 * tests for `PercentStrategy`
 * addition of min/max values
 * optimization of default percents
 * other strategies?

/cc @kennethgillen @sbesson @manics @rleigh-dundee @stick @bpindelski