Delete local version of remote scrapers with priority 0 on update

[dstillman]

(In [958]) Closes #331, Allow phrase searching from quicksearch
Closes #318, Use word index if available to narrow search scope of fulltext scanner
Closes #420, Delete local version of remote scrapers with priority 0 on update

• Changed ZoteroPane.buildItemContextMenu() to make updates easier
• Changed inTransaction repository update delay to 10 minutes
• Fix fulltext search of text files with MIME types that don't begin with 'text/'
• ZoteroPane.setItemsPaneMessage(msg) and ZoteroPane.clearItemsPaneMessage()
• New textbox binding conditional-timed-textbox to run a test (e.g. on the value) before triggering command
• Fulltext content search now supports ANY/ALL instead of just AND (I think)