fix: datasources cancel button

[jacovinus]

This changes the way datasources settings are stored

• Previously the datasources fields were changed automatically without the option of a cancel button and aborting changes

For the new changes we will have a 'Cancel' button to set back all the fields to its initial values

• adittionally will have a confirm on save dialog to confirm changes made on datasources settings
• adds a cancel button to go back to previous settings
• added Import JSON functionality

Refs: #455
Refs: #501