RTLSDR and PlutoSDR bug fixes
- RTLSDR: fixed the GUI not taking the device RF gains into account preventing gain setting from the GUI. Fixes issue #63
- PlutoSDR: remove from the list of devices if it cannot be opened (already open in another instance or software)
Windows build
Return of the Windows 64 build. Built on Win7 with a new toolchain with Qt 5.9.1 and gcc 5.3.0