Abstracted out BasicButton and BasicToolbox Forms/displays.

[doylejd]

• Abstracted out the BasicButton and BasicToolbox forms to allow for reuse in field/block
• Abstracted out displays for BasicButton and BasicToolbox to allow for reuse in field/block
• Updated Block settings form to allow for Type selection and conditional display of subfields
• Updated Block/Fields Form and Display functions to call shared functions
• Hooked up Services validation function for the BasicToolbox form

[doylejd]

Resolves issue #20

[nerdstein]

This needs to go into a controller class

[nerdstein]

@doylejd - big things from my review:

1. module files should only contain hooks, all custom callbacks should be in controller classes
2. The 'AddThis' class itself looks like a potential controller.

Controllers should go into src/Controller

[doylejd]

@nerdstein Added comments and refactored code based on standards.

Investigating Controller classes and the ability to move the validate function. Additional refactoring may be needed. If so, I will open new issues for it.