refactor

* Split `FS.get` into client/server code `FS.File._get`
* Let get take `options` instead of arguments and remove argumentParser
dependency
* Updated documentation on `url` and `downloadUrl`
* Added note on the TempStore for discussion about improvements - not
critical to api
Add sa note
Base the upload queue on PowerQueue sub queues
minor fixes and code improvements; track uploading files by both collection and ID since one queue handles all collections
add strong reactive-list dependency for powerqueue
rewrite getExtension so it works for unmounted files, too
isEmpty will be true for null or undefined
do the isImage test correctly; add some API docs
fix several issues, make downloading work, improve a few bits of code
improve memory management, attempt client side resume implementation, other minor fixes
Switch to MicroQueue
Optimize buffer handling
Merge changes
Don't queue ddp method calls