Unification of the WPS tags description (FS#9618)

[Al Le]

After the description of the action upon file selection has been unified 
(with FS#10038), I'd like to draw your attention to a similar patch. It 
unifies the descriptions of WPS tags.

As of now, some WPS tags are described with just what the tag produces 
(e.g. "Current track"), others use the phrasing like "Display the 
current track." The patch unifies the descriptions, now we just tell 
what the tag produces, the words "Display"/"Show" are dropped.

What do you think? Is it worth to commit it?