suggestion: a better select-month emitter

[alexfung888]

Bug, feature request, or proposal:

proposal: returning month in a more useful format

What is the expected behavior?

returns '2017-03' instead of

What is the current behavior?

start=2017-03-01 0h0m0s local time
end= 2017-03-31 23h59m59s local time

What are the steps to reproduce?

switch to month mode and choose a month

Providing a Plunker (or similar) is the best way to get the team to see your issue.
Plunker template: http://plnkr.co/edit/o077B6uEiiIgkC0S06dd

What is the use-case or motivation for changing an existing behavior?

for easier extracting month/year of the selected month. Start/End is tricky, because ISO-STRING uses GMT and either start/end can easily move to previous/next month.

Which versions of Angular, Material, OS, browsers are affected?

any

Is there anything else we should know?

suggested code:

      newPeriod = {
        type: 'month',
        startDate: new Date(momentConstructor(entry.date).startOf('month').toDate().valueOf()),
        endDate: new Date(momentConstructor(entry.date).endOf('month').toDate().valueOf())
      };

      // add a new @output() selMonth:
      let sd = new Date(entry.date.valueOf() - entry.date.getTimezoneOffset()*60000);
      this.selMonth.emit(sd.toISOString().substr(0,7));