Add query filtering.

[connormanning]

This PR allows Mongo-style comparison query operators and logical query operators to be passed to read requests to filter data. Filters can apply arbitrarily nested logic to select points, and are passed via the filter query parameter.

An error handling case has also been improved, and a case that could cause streaming to hang has been fixed.

Samples: Select a tile by its origin ID:

filter={"Origin": 5}

Select a tile by a substring of its original path:

filter={"Path":"tile-845.laz"}

Select multiple tiles with classification filter:

filter={"Path":{"$in":["tile-845.laz", "tile-846.laz"]}, "Classification":{"$ne":18}}

Logical OR:

filter={"$or":[
    {"Red":{"$gt":200}},
    {"Blue":{"$gt":120,"$lt":130}},
    {"Classification":{"$nin":[2,3]}}
]}