Update the titles of the message windows in the Add-on Store

[CyrilleB79]

Link to issue number:

None

Summary of the issue:

When migrating an add-on update for which the version cannot be compared, the title of the confirmation dialog is "Add-on not compatible"; this is somewhat confusing because the add-on being installed may be compatible.

Description of user facing changes

Changed the title of this dialog with "Install add-on", as it is done for the "Remove add-on" action.

While at it, changed the title of other confirmation dialogs in the add-on store with the action being performed.

Description of development approach

Changed the strings in the code.

Testing strategy:

Manually tested messages

Known issues with pull request:

None.

Code Review Checklist:

• Documentation:
  • Change log entry
  • User Documentation
  • Developer / Technical Documentation
  • Context sensitive help for GUI changes
• Testing:
  • Unit tests
  • System (end to end) tests
  • Manual testing
• UX of all users considered:
  • Speech
  • Braille
  • Low Vision
  • Different web browsers
  • Localization in other languages / culture than English
• API is compatible with existing add-ons.
• Security precautions taken.