use custom grammar file for speech-to-text sample

It makes the sample more accurate (no more 'read' != 'red')
A customer is asking for a demo of a custom grammar file
make whitespace consistent
make sample more user-friendly

Add a text prompt that tells the user of the sample what they need to do
next.

Let the user specify when they want to stop recording, instead of
forcing them to wait five seconds every time.
Fix (apparently harmless) error

Whenever I debug unity from MonoDevelop, it would show an error
indicating that it couldn't load a project file. While the error was
apparently harmless, it could confuse customers. This checkin removes
the error.
fix cut-n-paste doc bug

Several unrelated methods claimed (in an exception description) to
require SMS scope. Changed them to the correct scope per method.
saving work in progress
don't try to access non-existent response
don't show generated files
use custom grammar file for speech-to-text sample
Merge branch 'use-grammar-file' of https://github.com/attdevsupport/ATT_APIPlatform_Unity_SDK into use-grammar-file
remove Avatar sample