Added new default tag attributes defaulting architecture

[ksevksev]

I added new default tag attributes defaulting architecture. It includes a new defaultTagAttributes property added to the taOptions object. When coding new defaults for an HTML tag, you:

1. add an object to taOptions.defaultTagAttributes as a new attribute that has the same name as the HTML attribute and includes attributes with names corresponding to the HTML tag attributes you're defaulting. The values for these attributes are the default value for the corresponding attributes.

For example: ...
defaultTagAttributes : {
a: {target:""}
},
...

means that when 'a' tags are put into the document they will be defaulted with a target value of "".

1. Alter the code that deals with that tag to use the defaults (or overridden defaults) found in the editor scope defaultTagAttributes property.

Users can override these defaults by passing a similar object to the textAngular (text-angular) directive as the taDefaultTagAttributes (ta-default-tag-attributes) attribute. This attribute extends the taOptions.defaultTagAttributes value that is then used when creating tags.

[ksevksev]

Updating the code to use angular.merge will improve the functionality of this feature allowing users to override tag defaults on an individual attribute level, rather than on a tag level.

[coveralls]

Coverage remained the same at 100.0% when pulling 2c8c2c9 on ksevksev:master into 7ee680d on fraywing:master.

[ksevksev]

This is my first github pull request, so please assume so if something is out of order. Just let me know and I'll make the necessary adjustments. Speaking of which, I committed all changed files, which includes generated files (textAngular.js, & minified files, etc.). Please inform me if I need to commit differently, so that you only get the actual 'source' code changes. Thanks! Ken