Even after cdf9d7ff32, the tag selector was still being initialized if
it was closed at startup, which meant that keeping it closed didn't fix
performance problems in large libraries. This hopefully finally brings
the tag selector in line with pre-Reactification behavior.
This also moves initIntlStrings() logic to Zotero.Intl so that strings
are accessible from React components in separate windows, and it moves
container initialization to ZoteroPane since most of what it does will
need to interact with ZoteroPane anyway.