DateTextBox: automatically display dropdown

[bill]

Rather than having a drop down arrow, automatically display the calendar whenever you focus on a DateTextbox?. Clicking a date on the calendar closes it (and copies the value to the DateTextbox?), but you can reopen the calendar by clicking the DateTextbox?.

This seems better usability-wise and also helps with InlineEditBox? usability (see #3514).

[haysmark]

Something to consider: slightlyoff was originally complaining about Tooltips obscuring the save and cancel buttons, and that you had to click outside of the textbox to make the Tooltip go away so you can see the save and cancel buttons. I'm worried that the same thing will happen again, and this time with the much larger Calendar, if you make this change to DateTextbox?.

[bill]

Right, I guess this has to be done in tandem with removing the save/cancel buttons altogether.

[bill]

(In [9297]) Modify DateTextBox? to show drop down automatically on focus or click, and to close it when you select a date, focus on another field, or click in a blank area of the screen.

Fixes #3516.

Still need to update InlineEditBox? to not display save/cancel buttons for DateTextBox? (or alternately put them on the right, but that precludes the use of validation messages, which are important since non-mouse users need to enter dates directly into the <input>, rather than picking them from the calendar).