Fix parsing URLs with no parameters.  Add isEmpty and remove methods.
Add UrlParams unit tests
Fix parsing edge cases and added edge case tests
Fix _store initialization in public method parse()
Merge pull request #6246 from lkcampbell/fix-6008

Fix UrlParams parsing when URL has no parameters.  Add remove() and isEmpty() methods.
Merge branch 'master' of https://github.com/adobe/brackets