New frequency scanner plugin

New frequency scanner plugin

Thanks to @srcejon for this new Rx channel plugin. See https://github.com/f4exb/sdrangel/tree/master/plugins/channelrx/freqscanner

Other changes and fixes

• Implementation of Mac OS CI. PR #1841 from @srcejon
• Change down and up channelizers filter chain strategy. Fixes #1846
• Fix race condition that can result in a crash or hang. PR #1854 from @srcejon
• DSC Demod: initialise m_scopeSink. PR #1854 from @srcejon
• Fix FFT Overlap for spectrum view. PR #1856 from @das-Iro
• Various ADS-B enhancements. PR #1861 from @srcejon
• Use channel sample rate of 48k in RTTY and PSK31 mods. Fixes #1862. PR #1865 from @srcejon

Binary artifacts

For more details on artifacts and their contents please read the quick start in the Wiki.
Note that Ubuntu .deb package is for 22.04. Please note that SSE 4.2 is required.