Don't use native menu bar on Linux
Don't use native menu bar on Linux

Fixes Issue #542

cfelipesouza/qgroundcontrol,caoxiongkun/qgroundcontrol,catch-twenty-two/qgroundcontrol,LIKAIMO/qgroundcontrol,jy723/qgroundcontrol,scott-eddy/qgroundcontrol,hejunbok/qgroundcontrol,remspoor/qgroundcontrol,CornerOfSkyline/qgroundcontrol,dagoodma/qgroundcontrol,hejunbok/qgroundcontrol,hejunbok/qgroundcontrol,devbharat/qgroundcontrol,cfelipesouza/qgroundcontrol,scott-eddy/qgroundcontrol,iidioter/qgroundcontrol,mihadyuk/qgroundcontrol,caoxiongkun/qgroundcontrol,fizzaly/qgroundcontrol,LIKAIMO/qgroundcontrol,iidioter/qgroundcontrol,remspoor/qgroundcontrol,cfelipesouza/qgroundcontrol,mihadyuk/qgroundcontrol,CornerOfSkyline/qgroundcontrol,TheIronBorn/qgroundcontrol,lis-epfl/qgroundcontrol,ethz-asl/qgc_asl,BMP-TECH/qgroundcontrol,lis-epfl/qgroundcontrol,devbharat/qgroundcontrol,CornerOfSkyline/qgroundcontrol,nado1688/qgroundcontrol,fizzaly/qgroundcontrol,scott-eddy/qgroundcontrol,BMP-TECH/qgroundcontrol,kd0aij/qgroundcontrol,TheIronBorn/qgroundcontrol,fizzaly/qgroundcontrol,greenoaktree/qgroundcontrol,ethz-asl/qgc_asl,scott-eddy/qgroundcontrol,devbharat/qgroundcontrol,CornerOfSkyline/qgroundcontrol,lis-epfl/qgroundcontrol,remspoor/qgroundcontrol,kd0aij/qgroundcontrol,greenoaktree/qgroundcontrol,jy723/qgroundcontrol,josephlewis42/UDenverQGC2,catch-twenty-two/qgroundcontrol,TheIronBorn/qgroundcontrol,caoxiongkun/qgroundcontrol,caoxiongkun/qgroundcontrol,catch-twenty-two/qgroundcontrol,CornerOfSkyline/qgroundcontrol,dagoodma/qgroundcontrol,RedoXyde/PX4_qGCS,CornerOfSkyline/qgroundcontrol,josephlewis42/UDenverQGC2,BMP-TECH/qgroundcontrol,devbharat/qgroundcontrol,ethz-asl/qgc_asl,Hunter522/qgroundcontrol,UAVenture/qgroundcontrol,LIKAIMO/qgroundcontrol,ethz-asl/qgc_asl,caoxiongkun/qgroundcontrol,RedoXyde/PX4_qGCS,TheIronBorn/qgroundcontrol,cfelipesouza/qgroundcontrol,kd0aij/qgroundcontrol,greenoaktree/qgroundcontrol,josephlewis42/UDenverQGC2,nado1688/qgroundcontrol,Hunter522/qgroundcontrol,LIKAIMO/qgroundcontrol,jy723/qgroundcontrol,devbharat/qgroundcontrol,RedoXyde/PX4_qGCS,caoxiongkun/qgroundcontrol,Hunter522/qgroundcontrol,josephlewis42/UDenverQGC2,Hunter522/qgroundcontrol,fizzaly/qgroundcontrol,kd0aij/qgroundcontrol,LIKAIMO/qgroundcontrol,RedoXyde/PX4_qGCS,BMP-TECH/qgroundcontrol,mihadyuk/qgroundcontrol,kd0aij/qgroundcontrol,hejunbok/qgroundcontrol,dagoodma/qgroundcontrol,hejunbok/qgroundcontrol,LIKAIMO/qgroundcontrol,mihadyuk/qgroundcontrol,mihadyuk/qgroundcontrol,dagoodma/qgroundcontrol,UAVenture/qgroundcontrol,Hunter522/qgroundcontrol,UAVenture/qgroundcontrol,lis-epfl/qgroundcontrol,UAVenture/qgroundcontrol,BMP-TECH/qgroundcontrol,iidioter/qgroundcontrol,jy723/qgroundcontrol,BMP-TECH/qgroundcontrol,dagoodma/qgroundcontrol,remspoor/qgroundcontrol,catch-twenty-two/qgroundcontrol,devbharat/qgroundcontrol,fizzaly/qgroundcontrol,RedoXyde/PX4_qGCS,RedoXyde/PX4_qGCS,catch-twenty-two/qgroundcontrol,fizzaly/qgroundcontrol,hejunbok/qgroundcontrol,jy723/qgroundcontrol,nado1688/qgroundcontrol,Hunter522/qgroundcontrol,scott-eddy/qgroundcontrol,cfelipesouza/qgroundcontrol,jy723/qgroundcontrol,UAVenture/qgroundcontrol,scott-eddy/qgroundcontrol,lis-epfl/qgroundcontrol,iidioter/qgroundcontrol,TheIronBorn/qgroundcontrol,iidioter/qgroundcontrol,greenoaktree/qgroundcontrol,ethz-asl/qgc_asl,remspoor/qgroundcontrol,nado1688/qgroundcontrol,UAVenture/qgroundcontrol,catch-twenty-two/qgroundcontrol,TheIronBorn/qgroundcontrol,iidioter/qgroundcontrol,dagoodma/qgroundcontrol,remspoor/qgroundcontrol,cfelipesouza/qgroundcontrol,nado1688/qgroundcontrol,greenoaktree/qgroundcontrol,nado1688/qgroundcontrol,mihadyuk/qgroundcontrol,greenoaktree/qgroundcontrol,kd0aij/qgroundcontrol