Outputs Update #2 - Run Gudrun in Temporary Directory

[rhinoella]

Stage 2 of Outputs Update #457, builds off of #458.

This PR changes the way gudrun_dcs is run, by running it in a temporary directory, so all the files are outputted there, and then organising and copying the outputs back in the user's permanent directory.

This approach has three advantages:

• Removes the need for dangerous file-management operations (folder/file deletions) in the permanent directory
• If the program crashes or there is an issue with the run there will be no unorganised files to manage
• Much more control on how to present outputs to users and choosing save locations

Changes

• Gudrun and Purge DCS are run in a temporary directory
• The running of the process is done using a QThread and a worker instead of a QProcess as this allows for the use of a context manager
• Purge dialog is changed - no longer asks to run with default parameters (the user can just click 'OK' for this)

Next Steps:

• Update Batch Processing to utilise the new system- remove dcs() function
• Deploy GudPy class to handle all the GudPy processes (remove responsibility from GudrunFile class)
• Add new functionaity to headless mode
• Import project from project folder