#25757 Commands to move a localized core out of a config

Adds the two following commands to the tank command line:

```
share_core
----------
When new projects are created, these are often created in a state where each
project maintains its own independent copy of the core API. This command
allows you to take the core for such a project and move it out into a separate
location on disk. This makes it possible to create a shared core, where
several projects share a single copy of the Core API. Note: if you already
have a shared Core API that you would like this configuration to use, instead
use the attach_to_core command.

attach_to_core
--------------
When new projects are created, these are often created in a state where each
project maintains its own independent copy of the core API. This command
allows you to attach the configuration to an existing core API installation
rather than having it maintain its own embedded version of the Core API. Note:
If you don't have a shared core API yet, instead use the share_core command.
```

Technically we should be using sys.platform.startswith("linux") for python 3 compatibility.