Include dateDecided, dateEnacted, issueDate in "Title, Creator, Year"

Allow searching for dateDecided (case), dateEnacted (statute), issueDate (patent) in the "Title, Creator, Year" quicksearch mode. It's also very useful in the Quick Format Citation dialog.

http://forums.zotero.org/discussion/23597/ yes, that's my own ~~bug report~~ request ;-)

(I added a <code>if</code> without <code>else</code> -copied from the preceding twenty lines- and I don't know if it's a good practice (?)... but the condition should always be met.)