Bumping CMake minimum to 2.8.8 as agreed

This was discussed on the mailing list a few months ago.

Change-Id: I9a7d81fd3fb94827b1eab9f2e21ef965b05ebb09
Resolve valgrind defects

Initialize Position in the constructor of vtkColorLegend
to avoid uninitialized memory reads.

Change-Id: Ide2da0c7dac74d10aa17a1c525f61a6c13887208
Merge topic 'fix_charts_valgrind' into master

9f5eb493 Resolve valgrind defects
Merge topic 'bump-cmake-requirement' into master

eee9f52c Bumping CMake minimum to 2.8.8 as agreed