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
I wouldn't go full hog on `perm_gen` but there is certainly room for improvement beyond 256MB. It's one of those settings which comes more into play the longer a server runs. So a small, dev installation at 4GB, or whatever, will initially be fine with a low setting. After a while, it will become unhappy. Therefore on a system that can afford to spend more on the perm gen, I'd give it. (Not saying these values are perfect yet, just that there is some room for bumping it. It's exactly what we do on our production systems anyway)