FileListControl adjustments

* Changed button bar layout to be et the end, rather some-what in the
middle
* Make SelectPathInputDialog remeber previously entered path
* Make workspace selection dialog set proper initial selection, even if
this widget runs without cdt context

Change-Id: I04caec8c05b644977ec0dda622beefa2b8c9eba2
Signed-off-by: Alena Laskavaia <elaskavaia.cdt@gmail.com>
Reviewed-on: https://git.eclipse.org/r/37032
Tested-by: Hudson CI