Description of problem:
For intuitive minimal platform installation it is required to add deselect all button to anaconda installer. This option would deselect all package groups selected by default and installew would be only @core - which is minimal platform.

Version-Release number of selected component (if applicable):
12.36

How reproducible:
always

Steps to Reproduce:
1. During package customization pres deselect all
  
Actual results:
No deselect all button

Expected results:
Deselect all button available

Additional info:
This bug is reported as a needed feature after fixed comps, see https://bugzilla.redhat.com/show_bug.cgi?id=485995#c24