Allow selection of default tool when program opens with new image.

[RCAFinfo]

Description
Currently Pinta does remember the last tool that was used which works good for some work flows. However with some work flows it would be beneficial to have a specific tool set as default every time a new image is opened. For example I would love the default tool in my installation be set to Rectangle select. For others this may be another tool.

Additional context
Comment from cameronwhite "The preference needs some more thought since we generally aim for simplicity vs having big configuration dialogs, so I'd probably lean more towards e.g. right clicking on the tool to configure that preference"