Documentation fix in https://atlas.apache.org/TypeSystem.html and http://atlas.apache.org/InstallationSteps.html

In https://atlas.apache.org/TypeSystem.html, under "System specific types and their significance" >> DataSet, Dataset is defined as "This type extends Referenceable", but Dataset actually extends Asset, which in turn extends Referenceable. 

Replaced all 1.0.0 reference to 2.0.0 in http://atlas.apache.org/InstallationSteps.html