feat: add option to include the current session in load_session UI

[fleesk]

Added the option load_include_current, which defaults to false, to allow the currently opened session to be included in the load_session selection.

Use Case

This use case may be very specific to me. I often find myself straying from the files in the initial sesssion, such as changing something in my config while in a session specific to another project, and I end up doing entirely different things in buffers unrelated to the original project session.

Solution

• The previously loaded session appears in the load_session UI if the new config option, load_include_current (should probably be renamed to something more succinct)
• When re-loading the same session, it is not saved before reloading (as is usually the case when switching sessions), so I get back to where I started

[Shatur]

Thanks! Left a few nitpicks.

[fleesk]

Thanks, I integrated your changes