Perform reads in a thread so File I/O does not block.
This patch also disables ETags for static files. Tornado's default behavior of caching file hashes will not work as many of Moonraker's can be updated. The previous workaround to this was to recalculate the checksum if the modified date changed. This is inefficient as its behavior is not much different than using "If-Modified-Since".
Signed-off-by: Eric Callahan <arksine.code@gmail.com>
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