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`~~ (done)
 * addition of min/~~max~~ values (max done)
 * optimization of default percents (**in-progress**)
 * ~~other strategies?~~ (adaptive added; suggestions welcome)

/cc @kennethgillen @sbesson @manics @rleigh-dundee @stick @bpindelski
If the server can actually run okay with 256MB permgen is it plausible that it will ever use much more if available?