For issues #99, #100, #112, and #120

[mhmdkrmabd]

• Import workspaces feature:
  • Added the ability to import workspace(s) by simply selecting or drag-and-drop workspace(s) folder.
  • The app will filter given folders and keep the valid healthy ones, missing variables and duplicate names are checked against each workspace.
  • The user can select which workspace(s) to be imported, and which cluster(s) to be imported inside each workspace.
• Improvements to the variables feature
  • The name of the variable can only be letters and digits - preparation for nested variables -.
  • The app now detects missing variables in each added cluster and provides the ability to the user to adopt them with set values.
• Checking Cassandra node inside Docker will be every 10 seconds instead of 20.
• Minor changes and updates, and limited refactoring process.