Implement Web Share API in share timetable modal

[ZhangYiJiang]

Chrome Mobile 61 implements a new way to access native sharing dialog via the Web Share API. This API is not well supported outside of Chrome, but Caniuse indicates the next version of Safari may also implement this. Since the API looks relatively straightforward I think we can try implementing this.

The change should be made to the share modal. The headings will probably need to be changed, although I'm not entirely sure what would be good - maybe replace both columns on the right with a single share button if native share API is detected?

[aaditkamat]

I would like to try working on this issue.

[ZhangYiJiang]

@aaditkamat Yeah, absolutely! Sorry I didn't notice this earlier. You don't need our permission to start on any of these issues :)

[shimeilee]

@aaditkamat Hi are you still working on it? :)

[aaditkamat]

Hi @shimeilee, I'm not currently working on this. You can take up the issue if you like.