REACH-115 Separate SaveUploader into Model layer and View layer

`BaseSaveUploader` is base class for `NWKSaveUploader` one. `BaseSaveUploaderView` isn't base for `NWKSaveUploaderView`.
@marimano, You might consider instead using the FileSaver.js library that is already part of flood.  It is a very robust library for downloading files that works across browsers (your approach will not work in Firefox).  I've created a separate task for this:

http://adsk-oss.myjetbrains.com/youtrack/issue/REACH-135