Add support for Activity intent filters and attributes.

* Adds support to parse the action and category elements in the
  intent-filter nodes in the AndroidManifest.xml

* Add all of the attributes in the Activity to ActivityData.
  Use a Map instead of individual fields to simplify parsing attributes,
  without having to explicitly set anything.

* Extend ActivityData with accessors for all activity attributes.

    * Adds a method for each attribute in the activity element.
    * Boolean attribute types are returned as booleans not strings.
    * Provides nominal support for xmlns -- doesn't assume all attributes
      are called 'android:<ATTR_NAME>'

Closes #957.