Fix l10n x vocabulary edit layout style

The tree to select entry parent has some style issues:

• node are not properly aligned
• cursors on tree node is not good
• when too many entries, there's no scroll bar and the dialog height is bigger than the window

See attached screenshot

Steps to reproduce:

• Login as Administrator
• Go to the Admin menu
• Click Vocabularies
• Select l10ncoverage
• Click Add entry
• In the opened dialog, click Select parent
• unfold europe (scrolling KO)
• create a new entry under France or any other country
• see that the France node alignment (the fold/unfold arrow) is KO