reports need to export child items independently from parent items

[erazlogo]

Basically, reports need to be consistent with collections--currently child items don't belong in reports just as they used not to belong in collections--only parent item types can be selected for export. See these forum posts:
​http://forums.zotero.org/discussion/705/working-with-notes/#Item_22
​http://forums.zotero.org/discussion/867/notetaking-capabilities-and-request-for-recommendations/#Item_11

[dstillman]

Child items should also display any tags they have.

[dstillman]

(In [1689]) Closes #654, reports need to export child items independently from parent items

Two options currently only available via about:config, combineChildItems and includeAllChildItems (which really means "Include All Child Items If Only Parent Items Are Selected")

Other changes:

• Moved Zotero.Utilities.cleanString() functionality to ZU.trimInternal() and created a regular trim() too that doesn't consolidate internal whitespace.
• Removed Zotero.getAll(), replaced with Zotero.Collection.getChildItems() and a new onlyTopLevel flag to Zotero.Items.getAll(). Also removed unused Zotero.getAttachments.
• Fixed XML parsing error during report generation when a long URL contained a trailing space