Implemented playing of local video files

[jellemdekker]

Implemented playing of local video files that users can select from their computer through a file selection window. Implements issue #99.

Preferably, the code could be cleaner, but right now it just works. 😄

[Joshfindit]

@jellemdekker How does the person at the other end sync playback? Do they need to have it at the same path, with the same filename? Could they prompted to choose the folder/file before playback can start?