HTML5 datetime input

[jhaiduce]

This PR modifies the DateTimeInputWidget to use HTML5 date/time input types on browsers that support it.

[stevepiercy]

This PR needs to pass all tests and linting before it can be merged. But before you work on that, note that we are moving to Bootstrap 4 in Deform 3.0. If people want to maintain Deform 2.0.x with Bootstrap 3, I can create a branch that can be actively maintained by whoever wanders by. All new development and maintenance is focused on Bootstrap 4 and Deform 3.0.

Also note that we will likely use a different datetime picker. One option is Flatpickr as mentioned in #405.

[stevepiercy]

I've merged the two PRs referenced above into master. You will could either:

• rebase this PR on master, then push to this PR
• create a new branch off of master and create a new PR, closing this one

[jhaiduce]

I've merged the two PRs referenced above into master. You will could either:

* rebase this PR on master, then push to this PR

* create a new branch off of master and create a new PR, closing this one

I decided to do the former, since I don't have a requirement to use Bootstrap 3.

Tests pass on my local machine, now waiting to see if Travis finds any problems.

[stevepiercy]

@jhaiduce this looks good with only one minor change.

If you have not already done so, would you please sign https://github.com/Pylons/deform/blob/master/CONTRIBUTORS.txt and push to this PR?

After that I will merge. Thank you!

[jhaiduce]

@jhaiduce this looks good with only one minor change.

If you have not already done so, would you please sign https://github.com/Pylons/deform/blob/master/CONTRIBUTORS.txt and push to this PR?

Done. Thank you!

[stevepiercy]

Thank you!