implement allow_era_choice wml for sp settings
disable allow_observers option for sp
fix getting value of checkboxes in sp settings
add "show_configure" and "show_connect" wml

in [campaign] tag. these can be set to a boolean (locked value) or "user" (user selectable)
remove hybrid campaigns from sp campaign list (mp)

now hybrid campaigns are only included in "campaign" list in mp create.
they are still added to the list of sp campaigns when in sp (since sp campaign select uses that list)
add era/mod define support to sp

I had previously forgotten to include this line.
remove IO_NONE in playcampaign.cpp
fix gui2 test for campaign_selection
add unit test for campaign_settings