Remove the ability to store project sesson files in geany.conf (i.e. remove the preference and enable it unconditionally, it's alredy on by default)

Well the option is to store them in project file or not `Edit->Preferences->Miscellaneous->Use project based session files`, but I guess the inverse could be taken to mean store them in `geany.conf`, except it doesn't control that, which is the point of the issue.

Personally I am happy to remove it and say project session files go in project files and non-project session files go in `geany.conf`, project files are really only named sessions, they are not much use without them unless someone has a reasonable use-case for not doing so?

Store session in geany.conf when opening a project Restore session when closing the current project

@kugel Looks like a good solution to me.

One thought is the need to try to avoid swapping to the geany session then back to another project session when swapping between two projects.