Revert "Session: Remove normalized name"

This reverts commit e50d59405d618e274d012f58f3517785290e3970.
Allow searching for a session by its path
Last session: Use session path
Oops...
Session: Add collation key for path.
Util: Copy GPtrArray-s.
Introduce a further abstraction of the session list.

This allows us to maintain a separate index used for path lookups and is
what we should have done from the beginning.

This project is a huge mess. Should probably have used C++ / something
else with OOP instead of good old plain C.
Allow session lookups by path
Copypasta made me forget semicolons.
Use the new session list abstraction
Remove unused variable
Fix syntax errors etc.