Use logRangesFlag in API, route reads based on TreeID (#671)

* Add helpers and refactor sharding package

- Adds a function to get a TreeID from an ID string
- Adds testing for the above
- Consolidates validation logic for UUID, TreeID, EntryID
- Removes code that attempts to use ActiveIndex() in the sharding
  package, as this is not accessible due to import cycles
- Other small cleanup and typo fixes

Signed-off-by: Lily Sturmann <lsturman@redhat.com>

* Change logRanges to work with int64

This is the type used by the trillian TreeID and saves from having to
convert in multiple places.

Signed-off-by: Lily Sturmann <lsturman@redhat.com>

* Add TreeID to LogInfo API endpoint

WARNING: breaks loginfo cmd to current prod server

Signed-off-by: Lily Sturmann <lsturman@redhat.com>

* Update API based on logRangesFlag

Signed-off-by: Lily Sturmann <lsturman@redhat.com>

* Use API's logRanges to retrieve artifacts

Signed-off-by: Lily Sturmann <lsturman@redhat.com>