[FEATURE] Storage of custom variables on FormComponents

This allows a "variables" property to be used on every Form component and ViewHelper. Setting an array of variables here, makes those variables available anywhere the Form object is available.

Can, for example, be used to store custom rendering instructions for the Preview section as described in #411
Merge pull request #412 from NamelessCoder/componentdatastore

[FEATURE] Data storage on Form components and ViewHelpers