Prevent UI from allowing invalid date intervals

Fixes issue #292.

I chose not to set readonly to the text inputs in the HTML so that
these fields can still work without javascript enabled.

If I were to set readonly to the datepicker inputs at document load and
mimic a clickable input through styling, I would have to override the
WordPress admin’ input[readonly]’ style with
    background-color: #fff;
But this assumes that clickable inputs will always have a background
colour of white.
Oops (missed a semicolon)
Merge pull request #298 from lukecarbis/issue-292

Prevent UI from allowing invalid date intervals
Simplifying DB update routine for media
Code formatting
Release notes for 1.2.8
Version bump to 1.2.8
Get title from parent object instead of get_the_title
Merge pull request #314 from x-team/issue-303

Get title from parent object instead of get_the_title
Release notes for 1.2.9
Version bump to 1.2.9
Merge pull request #2 from x-team/master

Update from remote