Little refactoring of client audio buffer setup.
Add RTTY mode.

There are assorted things wrong with it, starting with that it doesn't
work very well; therefore it's unconditionally disabled. This commit is
just to get the code available for further work and kept in sync with
the main codebase.
A client-side mic-input FFT display (no link anywhere yet).

This isn't really all that related to the rest of ShinySDR, really, but
it builds on the spectrum widgets, so here it is.
We're switching to space indents. Update style guide and linter config.
We're switching to space indents. Change indentation in all Python files.