Connect EditSingleParamDialog with ValueColorEdit

closes #194 (closed)

Beside connecting EditSingleParamDialog with ValueColorEdit, this MR has the following changes:

• Combine 'description' with 'instruction' in plot_type_info to remove redundancy.
• Add check in ValueColors string for number of valueColor, duplicated value, order of value
• Show error when checking ValueColors string the first time ValueColorEdit is created to help developer check if ValueColors that are added into DB not from the GUI are valid.