Simplesoapy

- allow setting gain to 0 dB in constructor

- use SoapySDR `getSampleRateRange()` method instead of `listSampleRates()` (if available)
- set total center frequency of the chain instead of center frequency of `RF` tunable element (this allows e.g. setting center frequency < 30 MHz on LimeSDR)
- `label` is now optional in `detect_devices()` function (fixes broken `detect_devices()` on USRP)

- specific fixes for RTL-SDR and SDRplay hardware quirks have been removed (fixed upstream), this also fixes problems with RTL-SDR on Windows
- new `list_stream_args()` method for listing stream arguments supported by device
- new `get_gain_range()` and `get_frequency_range()` methods
- allow setting `buffer_size` and `stream_args` in constructor and `stream_timeout` in `start_stream()` method
- use SoapySDR `getBandwidthRange()` method instead of deprecated `listBandwidths()` method, our `list_bandwidths()` method now returns list of ranges instead of list of discrete bandwidths

- allow getting and setting gain of specific amplification elements (`get_gain` and `set_gain` methods), you can also pass dict with specific gains to constructor (e.g. `gain={'LNA': 28, 'VGA': 12, 'AMP': 0}`)
- listing, getting and setting SoapySDR device settings (`list_settings`, `get_setting` and `set_setting` methods), you can also pass dict with specific settings to constructor (e.g. `settings={'biastee': 'true'}`)
- `stream` and `stream_timeout` are now public (it was `_stream` and `_stream_timeout` before)
- all properties (like `freq`, `sample_rate`, etc.) now returns actual values from device (not cached values)

- `detect_devices()` now outputs proper SoapySDR device args (use `as_string=True` argument to get device args as string)
- fix missing channel number in `start_stream()`
- add `list_channels()` method to list all available RX channels