Allow moving (instead of copying) files into Zotero

Cmd-drag on OS X, Shift on Windows and Linux

As requested in
https://forums.zotero.org/discussion/31717/delete-source-file-on-import/

Unfortunately due to https://bugzilla.mozilla.org/show_bug.cgi?id=911918
(and another issue on Windows) we can't show proper cursor feedback for
external file drags.
Fix cursor feedback for file drag-in on Linux, where we can set it
Fix merging of tags during sync conflict

If an item was added to a tag on one computer and another item was added
to the tag on a different computer, and then they both synced one of the
tags could be removed on the second computer to sync.
Use async storage mtime checking in Fx24 on Windows

https://bugzilla.mozilla.org/show_bug.cgi?id=899436 was backported to 24
Debugging for failed file downloads
Update renamed-styles.json

Updates from https://github.com/citation-style-language/styles/blob/master/renamed-styles.json
Look for abbreviations for longest possible match first
Don't drop last word when abbreviating journal names
Use the longest abbreviation possible.
E.g. Fictional journal "Journal of Annunc Materials" (obviously annunc is not a real word)
Use "annunc-":"annunc." substitution instead of "annu-":"annu." resulting in "J. Annunc Mater." instead of "J. Annu. Mater."
Abbreviate plural forms of words same as singular
If abbreviation is same as key, it's still valid
See http://forums.zotero.org/discussion/32000/overriding-automatic-abbreviations/
Merge pull request #392 from aurimasv/abbreviations

Fix abbreviation algorithm
Update maxVersion
Abbreviate word pairs (e.g. New York -> N. Y.)
Update abbreviations.json

Remove overrides for titles we now abbreviate correctly, and don't
delete potential prepositions that are rarely used as such in journal
titles ("hyphen", "midst", "minus", "modulo", outside", "pace", "past",
"plus", "round", "save", "til", "till", "times", "vice", "worth")
Fix name on abbreviations list
Don't fail during file upload if file doesn't yet exist
Show patents by issue date in timeline view
Fix "req is not defined" error message (which indicates a WebDAV error)
Fix cleanISSN