Implement networking

[ebanisadr]

This PR contains the vast majority of the network code we’ll need. Objects are synchronized via photon views, and their properties (i.e. position, rotation, color, etc.) can be synchronized via specific views (usually a Photon Transform View).

Objects that can be manipulated by any user (our goal) are strongly owned by one user in Photon land so I implemented a script called SharedObject which, when attached to an object, can be configured to allow the local user to take ownership of the object before manipulating it via Takeover(). This should be called before any other modifications to the object to ensure the local user has ownership of it.

Added functionality

• Users must now connect to a server before seeing our “classroom” scene.
• Photon integration has been added to the project.
• Users can manipulate generated objects once on the server, and other users will be able to see those manipulations.
• A Resources directory has been created to store objects that are created at runtime, on a server. This is because Photon explicitly says that’s the only way to do it.
• Drive by: android logcat has been added to the unity project to enable us to view printed logs (i.e. with Debug.Log(“msg”)

Known Issues/TODO items:

• The controller models and pen/eraser are shared between all players in a room rather than each player having their own. This is less of a concern for now because…
• Whiteboard drawings are not synchronized at all. I will implement this via RPC (rather than views) because its infeasible to transfer the textures over the network 10+ times per second.
• Users cannot enter their name before joining a room. I’m having trouble getting the onscreen keyboard to show up when a text input is focused, and it’s not so important because nameplates are not displayed yet either.
• Users do not have a model for their head or body.
• Users cannot leave rooms.
• Imported file contents are not networked at all.
• When joining a room fails the “Connecting…” message will remain on screen, rather than showing a failure message.

The TODO list is pretty long because I'm pretty incapable of manipulating scenes in Unity and/or they would require a lot of added complexity for this already-hefty PR. I'm also happy to be the "networking guy" going forward, and continue to work on these (along with voice chat and whatever networking is needed for features we add in the future).

[ApolloZhu]

Non-blocking issues (solve when we merge mvp into master, not necessarily introduced in this PR):

• AndroidLogcatSettings is still tracked. Might want to delete the file
• There's an extra GameObject in SampleScene, probably added when we are setting up the MVP branch
• Private/internal variable naming convention, e.g. multiuserScene -> _multiuserScene (see https://docs.microsoft.com/en-us/dotnet/csharp/fundamentals/coding-style/coding-conventions for the full style guide)