Improve compatibility and silent mode

[danijelt]

First commit improves compatibility (discussed in issue #7) with units that don't respond to RH, RI, Ra and RL queries. This should be a minimally intrusive way to do it, by moving them to a "failable" queries list. This way, we now always expect response from F9 (all of them should according to what I found online), and for units that don't return their external temperature there, we'll get it from Ra query anyway.

Second commit adds silent fan mode. Nothing special, just another value in enum. Tested and working.