Re-Factor code to Storage class

[FabioLuca]

Re-Factor code to Storage class

• Centralize the file path used in the project to be handled inside it.
• Add support to storing HTML files which are the result from the analysis, so they could be also stored in Dropbox.
• Add possibility to start and stop the Google Cloud SQL instance, to keep better cost control.
• Add error handling when the Google Cloud SQL is in stopped state.
• Add sorting by WKN and Date to the SELECT query for the conversion to Pandas