Provide Stash as a stand-alone installer

In addition to zip and tar.gz archives, several Atlassian products—such as JIRA and Confluence—are available as stand-alone installation packages. The installers include sensible defaults (which the user can override at install time) and a self-contained JRE.

Stash is only available as a zip/tar.gz archive which presents a few issues:

1. Users are independently required to install Java (meeting particular version requirements) at a system level. This may interfere with other services with Java dependencies on the machine.
2. In *NIX environments, users are independently required to create a dedicated system user for running Stash as a service. The JIRA and Confluence installers offer to create system-level 'jira' and 'confluence' user accounts for their respective services.
3. In *NIX environments, file and directory ownership of items in the tar.gz are a whatever uid/gid existed on the packaging system at time of creation ('jira' and 'root' in my expereince). This ties in with the previous point regarding system users.