Add 'is null'/'is not null' to user roles filter with a good description

Add an Output format for field: Comment: Approved and field: User: Active

#1396376 by pixelmord: Correct the checking for the default value of content has taxonomy terms with depth

#1395320 by dereine: Allow to use list human readable values instead of only machine key in argument summaries

#1137892 by agentrickard: Provide an area handler which allows to use some tokens(items per page, etc.) in the header/footer.

by dereine: Improve filter term_node by defining all used variables, removed unused variables and document much more stuff.