[BUGFIX] Show loading spinner when Updating TER list on search module

When you search for an extension in the Extension manager and then click
on the "Update Now" button to load the newest list from the TER, the
spinner was not displayed.

Also fixed some invalid HTML stuff and repositioned the spinner.

Resolves: #60600
Releases: 6.3, 6.2
Change-Id: I670d821248d14c0c1038b5995fc7daef2ead42d8
Reviewed-on: http://review.typo3.org/31864
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>