Add SponsorSidebar.
configparse: Defer timeinterval_fromstr import until runtime.

timeinterval_fromstr is implemented in Cython. ConfigParse is imported
in various plugin __init__s. This causes makefile issues on clean
builds.
No non-admin Promote_Graph.

Page was confusing/obsolete with switch to CPM.
Reword pref option to show self-serve advertising tab.