Change Lookup to respect ordering when returning keys or iterating through items
Optimize Lookup .indexOfKey(), since we use this every remove()
Merge branch 'develop-frontend' into feature/issue-412-lookup-keys-need-to-be-returned-in-the-correct-order
Minor changes to Lookup for better readability
Handle undefined items in Lookup .at() and .keyAt()
Handle bad keys in Lookup .at() and .keyAt()
Remove Lookup key indices lookup (I realised it doesn't offer any performance improvement, since we need to update the key indices lookup after each lookup)
Remove console.log debug statements (sorry)
Merge branch 'develop-frontend' of github.com:praekelt/vumi-go into develop-frontend