AutomergeText and Counter reflect any change to a doc

[heckj]

fixes #149 in the quickest, dirtiest way possible

• in the process of this, I expanded the scope (possibly stupidly) and updated the AutomergeText() initializers to establish schema if possible (no conflict allowed - won't change existing schema) when initializing with a path.
• updated the tests to show that a change happens, but it's basic and doesn't show that changes signals occur no matter WHAT change happened to a doc
• updated Tests to remove trackForLeak on AutomergeText and Counter usage since those now maintain a reference to the Document instance in order to watch for changes.