Allow ZeroClipboard DOM attributes to be more configurable.

* Adds new properties to the global configuration object: `containerId`, `containerClass`, `flashBridgeName` and uses them throughout the library instead of strings.
* Handle configuration of these values after ZeroClipboard SWF has been embedded
* Validate `containerId` and `flashBridgeName` against HTML4 Spec
* Updates ZeroClipboard.as to receive `SWF_OBJECT_ID` as a flashvar (`flashBridgeName`)
* Update docs
Merging PR #413.