FileManager - add to manage temporary and cached files

[smalers]

Need to implement a FileManager class and UI, which will manage the following:

• Temporary files, which can be deleted before and/or after the TSTool session. These files may be the result of data processing.
• Cached files, which may result from web service caching to ensure good performance for user interactions.

[smalers]

I committed initial work. Keep this issue open until the FileManager is fully functional.