Improve bidi & RTL support (#2415)

- Render cell text in its native direction
- Fix context menu positioning
- Fix item box (localizations needed)
- Fix column resizing
- Fix bidi text in collection tree
- Always right-align in RTL, always left-align in LTR.
  I'm going off advice from this excellent guide for RTL website design
  by Ahmad Shadeed: https://rtlstyling.com/posts/rtl-styling#tables
- Join creators in the tree ("Smith and Jones") using a format string to
  support languages like Arabic and Hebrew where there shouldn't be a
  space after the "and".
- Fix tabs
- Fix toolbar on Mac, flip icons on other platforms

test/tests/itemsTest.js

@@ -1116,7 +1116,7 @@ describe("Zotero.Items", function () {
 							}
 						]
 					),
-					'B ' + Zotero.getString('general.and') + ' D',
+					Zotero.getString('general.andJoiner', ['B', 'D']),
 					creatorType
 				);
 			}
@@ -1186,7 +1186,7 @@ describe("Zotero.Items", function () {
 							}
 						]
 					),
-					'D ' + Zotero.getString('general.and') + ' H',
+					Zotero.getString('general.andJoiner', ['D', 'H']),
 					creatorType
 				);
 			}