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

[jobara]

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

Additional context or notes

Originally filed as FLUID-5741 by @colinbdclark on August 12, 2015.