Removed a space
Add exception handling to AssetService

Make the AssetService return an empty string if the given asset isn't
found.
Make the root path redirect to "/feed"
Make FeedService filter out empty channel names

Fixes issues where the FeedGenerator would request feeds for empty
string channels. Such as "/feed" or "/feed/channel1++channel2" which
would request feeds for "" and ["channel1", "", "channel2"]
respectively.