Open key stores in an existing instance of KSE.

[jonwltn]

This PR implements #241 by opening key store files using an existing instance. If an existing instance does not exist, then it loads normally.

This PR reorganizes the auto reload settings and combines them with a new setting for opening files in an existing instance:

The first instance of KSE will open a unix domain socket (kse-ipc.sock) in the users temporary directory. This socket is always opened regardless of the configuration setting. Subsequent instances of KSE when opened with a list of files will attempt to send the list to an existing instance for opening and immediately close. If the existing instance cannot be contacted, then KSE loads and opens the files.

If the user preference setting is disabled, KSE will not check for an existing instance and will open the key stores using a new instance.

Limitations

• The KSE window is not brought to the top. If this is desired, we can use some Win32 (USER32.dll) calls for bringing the existing KSE instance window to the top.

Finally, this feature works on macOS, but it won't be used since MacOsIntegration manages the opening of files.