Fix OSGi default version, and more tests

I see Alex beat me to fixing this (see https://github.com/apache/incubator-brooklyn/pull/343).

I didn't know about `getCatalogItemOptionalVersion`, which makes it much simpler.

There are a couple of things in here that are still relevant and that I would like reviewed (I'll strip out the others later):
* Fix for Osgis.parseOsgiIdentifier(), so it does what it says.
* Use of 0.0.0_SNAPSHOT as default version is not a valid OSGi version number. Should we change it to 0.0.0.SNAPSHOT?
* Should we change the .js to use `/v1/catalog/entities/symbolicname/version`, given that the other method is deprecated?

@ahgittin @neykov remind me - is the catalog using OSGi version number, or maven-style version numbering with "-SNAPSHOT" suffix having special meaning (but using underscores instead)?
Use the versioned API where possible - "/v1/catalog/icon/" + details.getSymbolicName() + "/" + details.getVersion()

The current URL will return the latest item (not necessary the one we expect).