Blender Git Loki

RNA: Remove remaining relevant scene->basact and BaseLegacy

Note: In one case (rna_Scene_editmesh_select_mode_set) I had to resort
to the temporary solution of BKE_scene_layer_context_active.

This is fine for now, but it will be a problem once workspaces are
introduced. In this case the fix is to use a temporary value in the set
routine, and actually only set the active object in the update function
(which can take bContext).