add feature scaling for clustering

[alxndrkalinin]

Feature scaling is important pre-processing step for distance-based ML methods

• [x] read how Standardization works
• [x] create new service preprocessing and inject it into SidebarCtrl
• [x] service should provide method scale that implements feature standardization
• [ ] add scale method to [prepareData](https://github.com/SOCR/SOCRAT/blob/dev/app/scripts/analysis/tools/Cluster/ClusterSidebarCtrl.ctrl.coffee#L129) method after filtering out chosen features
• [ ] display switch in the sidebar allowing user to turn off standardization (should be ON by default), don't forget to add the label
• [ ] test that scaling works using Neuroimaging study of 27 AD, MCI, NC subjects dataset
• [ ] create pull request to SOCR/SOCRAT:dev