#108 provide pref for drop downs vs text box in edit posts screen

[Jayesh Sheth]

In the edit posts screen in the admin panel, there are
currently drop downs for the following fields:
keyword1, keyword2, keyword3, and category.

These dropdowns contain all the unique values in each
field.

Sometimes, with a large data set, it is desirable to
not have a drop dow box. In such a case, a simple input
text box is desriable.

Step 1: provide preferences in prefs.php or in a prefs
database table to control whether a drop down or text
box is shown for each field.

Step 2: incorporate a JavaScript autocomplete routine
for textboxes