Allow bootstrap to load blocks file on startup

[cromo]

One of the goals of FFF is to allow people to make their own applications and games from within VR, and to that end FFF should allow loading user code directly upon startup without having to go through the development environment layer. This means that the bootstrap layer will no longer be just a passthrough, but will need some way to determine when to run user code on startup.

The mechanism could be as simple as the presence of a single file that contains the name of the block file to load, which would allow multiple applications to be developed at once. This also means that it's easy to revert back to development mode by deleting this file, which can be done from within user code.

Should there be an escape hatch programmed into the bootstrap? Perhaps, but it should be user configurable; perhaps defined in the file with the block file name that the bootstrap would listen for.