[REFACTOR] Add `get-short-url` function
[REFACTOR] Add `get-short-url` function

containing the code which makes the ajax call to obtain a short url for
the current module selection.

Signed-off-by: Pang Yan Han <22594c345857f664c61cd411f607c4d40a9d4af9@gmail.com>

yanhan/cljs-nusmods,yanhan/cljs-nusmods,yanhan/cljs-nusmods