Video: Add custom layout for up to 8 participants.

This commit splits the video wall in regions according to the number of
participants. The custom layouts are 8 in total after which all
participants will be presented in a single row.
Video: Use solid background for the local video element.
app/modules/{webrtc.io => webrtc.io-client}
Modules: Handle dependencies at the module level.

This commit moves module-dependencies to the module itself rather than
the main project. The `make install-nodejs-dependencies` command has
been updated as well.
README: Update with quick instructions on running Ellenoir locally.