Refactor and normalize ngBolt component attributes

[theJuddson]

Refactor all usages of our internal blt attribute directive to use the built-in ng-attr directive. This should resolve some of the attribute related bugs that we've been experiencing. (Issues #34 and #30)

Ensure consistent attribute availability and binding across all components. Bind with one way model binding '<', when possible, falling back to DOM attribute binding '@' for components that will almost always be defined with a string literal. The goal here is to ensure that binding type ('<', '&', '@') is consistent for each attribute across all components, and avoid requiring the developer to use interpolation {{}} to provide attribute values whenever possible.

[theJuddson]

The components that will need to be refactored are:

• [x] Checkbox Radio
• [x] Counter
• [x] Date Picker
• [x] Dropdown
• [x] File Loader
• [x] Toggle Switch
• [x] Text Field

Text field has been completed already in the issue_34_attribute_refactor branch. Please use that component as a reference point.

The following attributes should be shared across all components. Please add/update all other components to include these attributes ensuring the binding is as specified here.

• name: '@'
• label: '@'
• model: '='
• change: '&'
• disabled: '<'
• tabindex: '<'
• autofocus: '<'
• required: '<' (excluding Toggle Switch)
• validate: '<' (this one may take additional work. see me for more details if necessary)

Several different components use 'min' and 'max' attributes. Please ensure that these are consistent with the Text Field.

You can also review the additional attributes that are specified on the Text Field component to see if any apply to other components, however most of them will not apply.