Add ability to share tours by url.

Add:
	app.py
		-change "/showDirections" route to "/tour/<tour_obj_id>" route, where
		<tour_obj_id> is the mongo object id of a document containing a complete
		(ie entirely preprocessed, with all necessary variables) tour
		dictionary.
		-allows users to share tours by url

	py/utils.py
		-add get_mongo_tour(), which finds a tour by its object id
		-add add_mongo_tour(), which adds a tour and returns its object id
Make tour loading smarter; fix contact js bug.

Add:
	app.py
		-whenever a user manually creates a tour (instead of accessing a premade
		tour by url), the full tour dictionary is stored in
		session["tour_dictionary"]. When the tour page is accessed, if
		"tour_dictionary" exists within the session then the tour has only just
		been created, and is simply loaded from memory; otherwise, it's queried
		for in the mongo tours collection. Precludes unnecessarily searching for
		a tour in our db when it was recently stored in a variable.

Fix:
	static/js/contact.js
		-fix button click bug, where clicking either the "email us" or "call us"
		button would change that button's style, but not the content
		displayed (either a phone number, or an email textarea).