Make folder to open directory lists and terminals configurable

[matthew-matvei]

Feature

As mentioned in #26, it would be useful to allow users to configure which directory is opened on application startup in the directory lists and terminals. The user should be able to configure different startup folders for the left and right components also. If this is not configured by the user, the app should open at the user's home directory. If the configured directory can't be successfully loaded, the home directory should be used as a fallback.

• User can configure a folder that the application uses to start up an integrated terminal in
• User can configure a folder that the application uses to start up a directory list in
• User can configure left and right directory lists / terminals separately
• Application falls back to user's home directory if loading configured directory fails (per component)