Preview section updates for improved usability

Several recommendations for the Preview part of the page.

1. Empty state:
Refer to https://www.patternfly.org/v4/documentation/react/components/emptystate/ You should be able to use the centered version of the empty state, and leave out the "action" button.
The text beneath "NO DATA AVAILABLE" could be updated to remind the user to select SAVE to save SQL statements in the editor before instructing them to Refresh. Confer with the doc specialist for specific wording on this.

2. Preview Results (icon):
Change the label "Preview Results" to "Refresh"

3. Indicate the number of rows:
In the demo, I recall that Ramesh said: "We are only showing 'x' number of rows in the preview." Would it be possible to bring the same labeling you use in the "SQL Client" tab to this page as well? That would result in a label above the preview letting the user know they are only seeing a subset – "Number of rows: 15" (or whatever the right number is). Otherwise, there is nothing in the UI that indicates that the user is only seeing a subset of items.