Better message display when fetching data

[atn38]

A couple refinements we might want to make:

• Make it more obvious that the data package is fetched and ready. As it is now, the fetching messages might run below the fold for larger packages, and the user isn't alerted that the download is completed. Proposed solution: remove the fetching message once complete and display a message prompting the user to choose a data object from the menu.

• Once the user has selected a data object, the messages are pushed below the data table. See picture. The above solution should also solve this issue.

[clnsmth]

Another option for point 1 is to reverse scrolling and print the most recent message to the top. This preserves potentially useful diagnostic messages delivered during loading.

[atn38]

in issue #91, the GUI still inserts the message Download and parsing is completed. Select a data object from the left menu to start. prominently despite download and parsing failure. It shouldn't do that. IIRC I wrote the logic to insert this message, so will need to fix.