Improve data explorer UI layout

[seancolsen]

Overview

This PR

• Moves the Data Explorer status bar below both sidebars
• Moves the refresh button into the status bar (to match the Table Page).
• Removes some arguably superfluous UI that felt especially awkward after moving the refresh button

Fixes #3183

Also helps mitigate #2354

Data Explorer

Before

After

Exploration Page

Before

After

Checklist

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[seancolsen]

@pavish please review code changes and UI/UX.

@ghislaineguerin please take a look at the UI changes here to make sure you're okay with them.

[seancolsen]

@ghislaineguerin and I went over this on a call and she said she's good with these changes.

[pavish]

@seancolsen Two minor comments, not worth blocking the PR - I'll leave it upto you to make changes/merge:

1. I noticed an edge case involving the refresh button:
   • Open an existing exploration.
   • Edit it by clicking the 'Edit in Data Explorer' button.
   • The exploration must have some results of rows. Notice the status bar showing pagination as expected.
   • 
   • Delete all columns.
   • Notice that in the status bar on the bottom, only the "Refresh" button is present.
   • 
   • Now, click the "Refresh" button.
   • Notice that the pagination components are present again even though there are no results.
   • 
   • This is because the API actually returns rows with empty objects with the count.
   • This is not an issue that arose from changes in this PR and the reason we didn't encounter this before is because the Refresh button was not present when there were no columns selected/no results.
   • We might want to consider hiding the Refresh button or making it disabled when there are no columns.
2. Since the placement of the status bar is quite similar to the table page now, it would be good if we made the height consistent in both pages.

[seancolsen]

Thanks @pavish

• I pushed 95ec390 to hide the refresh button when there are no columns. Nice catch!

• I pushed 04192ab to make the status bars the same height.