* add a little Stash utility.
* add radio state RAII helper.
* first part of radio_state changes
* add radio_state_ to rest of apps
* fix freq_step and format
* fix unused ui_sigfrx: corrected sample rate, added back freq setting
* Allow apps to not use persisted freq.
* use rx_freq for RX mode
* remove direct call to persistant_memory in tx_model
* app_setting defaults, and tx_view to use ctor value