refactored space-name validation tests for readability
refactored space-name validation tests for readability

While this introduces a (small) layer of abstraction in the tests, it
makes the tests more immediately grasp-able and maintainable

TiddlySpace/tiddlyspace,FND/tiddlyspace,TiddlySpace/tiddlyspace,FND/tiddlyspace,TiddlySpace/tiddlyspace,FND/tiddlyspace