Feature request: Check whether installation is complete.

[JackMostow]

Is your feature request related to a problem? Please describe.
A clear and concise description of what the problem is.
DriveSync had not finished downloading RoboTutor before installing it, so the installation was incomplete.

Describe the solution you'd like
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Check whether installation is complete.

Describe alternatives you've considered
A clear and concise description of any alternative solutions or features you've considered.
a. List and log contents of local Download folder to see if it was completely downloaded and up to date.
b. Upload DriveSync log to see if it completed.
c. Check at launch time if all assets are present and up to date. If not, display error message and crash or wait.
d. Compute checksum of robotutor_assets to compare to expected value.

Approach to be followed (optional)
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Additional context
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