Replace references to Infusion 2.0 with 1.9 in the infusion-docs 1.9.x branch

The 1.9.x branch of the infusion-docs repository still makes reference to Infusion 2.0. We should update it to refer to 1.9 instead, and to remove any "overly futuristic" references such as the "Component Grade Changes" on this page: http://docs.fluidproject.org/infusion/development/APIChangesFrom1_5To2_0.html