Set sbt version in build.properties file to be 0.12.4

This is a good practice, and it avoids breaking the build if you have a 0.13.0
sbt-launcher.
Renamed image for find occurrences
Added short documentation for Type Hierarchy
Added changelog entried for 3.0.2-RC1
integrated reviewer feedback
Merge pull request #79 from scala-ide/misc

Misc