Clone Timeline: Copy UI
Clone Timeline: Export Functionality

Allows a timeline (and any descendant timelines) to be saved to
localStorage, including each timeline's exhibits and their content
items.
Clone Timeline: Paste UI

Added paste validation that copied data is from same schema version.
Implemented API pass-through for paste, ready for paste functionality in
C#, which needs to include date bounds checks. (Clean.) Implemented
basic paste UI. Paste appears after copy to CZ clipboard. However,
currently need to refresh browser to see. (WIP.)
Clone Timeline: Import Functionality

Can now fully save off (export) a timeline, including exhibits, content
items and descendant timelines with same items, then import it into a
different timeline, even on a different account. This completes first
pass of export/import coding. Some rough edges, such as no auto-refresh
of canvas after exporting or importing.
Clone Timeline: Cleanup

Copy icon now available, even if not logged in. (Useful for grabbing a
subset of Cosmos such as "Humanity".)

Paste icon now hidden unless user has appropriate edit rights to
collection. Previously always displayed if user was logged in.

Quick workaround for displaying paste icon after copy without refresh:
If user has edit rights, now paste icon always displays alongside copy
icon. User is told if attempting to paste without first copying that
user needs to copy to clipboard first.

Per Lori, did not spend time on addressing auto-populating of newly
pasted content. A page refresh or URL change is still required, and the
user is informed of this when pasting.
Merge branch 'export-import' of git://github.com/NeilCresswell/ChronoZoom into NeilCresswell-export-import
Merge branch 'NeilCresswell-export-import'