Bug fixes and pre-request actions

• Changed actions panel to include pre-request actions (setting up variables)
• Updated post request actions: now you can iterate over response to find a value
• Fixed issue with error message thrown from main process about destroyed window
• Changed session management to only user Chromium's session to store cookies (removed ARC's cookie storage)
• Information about selected environment is now stored in workspace session file and is restored when re-opening the app.