Routing extensibility improvements

[richardgorman]

• [ ] Bug Fix 🐛 (non-breaking change which fixes an issue)
• [ ] New Feature 🚀 (non-breaking change which adds functionality)
• [ ] Breaking Change 💥 (fix or feature that would cause existing functionality to not work as expected)
• [ x ] Polish 💅 (Just some cleanups)
• [ ] Docs 📝 (Changes in the documentations)
• [ ] Internal 🏠 Only relates to internal processes.

[coveralls]

Pull Request Test Coverage Report for Build 1749

• 4 of 44 (9.09%) changed or added relevant lines in 15 files are covered.
• 55 unchanged lines in 6 files lost coverage.
• Overall coverage decreased (-0.7%) to 46.802%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
libraries/common/context/index.js	0	1	0.0%
libraries/common/selectors/router.js	3	4	75.0%
libraries/common/subscriptions/helpers/handleLinks.js	0	1	0.0%
themes/theme-gmd/pages/subscriptions.js	0	1	0.0%
libraries/common/actions/router/routeDidPop.js	0	3	0.0%
libraries/common/actions/router/routeDidPush.js	0	3	0.0%
libraries/common/actions/router/routeDidReplace.js	0	3	0.0%
libraries/common/actions/router/routeDidReset.js	0	3	0.0%
libraries/common/actions/router/routeWillPop.js	0	3	0.0%
libraries/common/actions/router/routeWillPush.js	0	3	0.0%

Files with Coverage Reduction	New Missed Lines	%
libraries/tracking/selectors/page.js	1	0.0%
libraries/common/selectors/router.js	1	68.09%
libraries/core/commands/openPage.js	2	0.0%
libraries/core/commands/showTab.js	2	57.14%
libraries/common/subscriptions/helpers/handleLinks.js	19	52.21%
libraries/common/subscriptions/router.js	30	36.54%

Totals
Change from base Build 1747:	-0.7%
Covered Lines:	4806
Relevant Lines:	9667

---

💛 - Coveralls