Stop flattening the tags to lowercase
Added case_sensitive property for streamer clauses

Now we can set case sensitivity for the streamer search properties. The clause evaluation in the FilterHandler class looks for this property and compares accordingly. The streamfilter.coffee was also extended to handle this new property.
Tagstream search is now case insensitive.
Userstream search is now case insensitive
Case insensitive uri filtering for notifications
Revert "Case insensitive uri filtering for notifications"

This reverts commit ec26ae5d89f66929935b8dc8f6ce4f62ab8dc40a.

uris can be case-sensitive
Merge pull request #659 from hypothesis/654-mixed-case-tags

Stream filters now handle both case sensitive and case insensitive searches.

Tags are case insensitive.

Fixes #654.