Introduce active editing window tracking system

Introduce real-time editing window tracking system (replaces current one), that works like this:

• each editing window is being registered in the memory table (session id, window id, user, item prefix, item id)
• each editing window periodically (configurable) reports back to inform, that it's still being opened
• upon window closing, (save button, cancel button, "X" icon) information about the editing window is immediately removed along with associated temporary tables
• a scheduled task periodically (configurable) looks for registered windows that failed (e.g. non-detected closed editing window) to report back and purges them (window record, temporary tables)