'dropdown' 'drop down' consistency in widgets

[trepmal]

In the Archives widget, there's an option to "Display as a drop down".
In the Categories widget, the same option is labeled "Show as dropdown"

Also, the "Show post counts" is the first option under for Archives, but the second for Categories.

[jane]

Let's use 'Display as dropdown' across the board.

Let's list dropdown before post counts.

[nacin]

(In [15993]) Standardize on 'Display as dropdown' and list those before post counts in default widgets. fixes #15096.