intro for concepts toc

Signed-off-by: Sam Kleinman <samk@10gen.com>
rs-reorg: edits to introductory blurbs
image to figure changes and update 'secondary-only' text

Signed-off-by: Sam Kleinman <samk@10gen.com>
DOCS-1492 review edits
minor: fixing xref issue
rs-reorg: edits

Signed-off-by: Sam Kleinman <samk@10gen.com>
theme: fixing jira collector problem
copy edits to param/field table changes for commands