Generate valid manifest for mbed library

[ivankravets]

1. There is an old-style version of mbed library. It does not contain module.json file. We should add recursively all libraries into http://docs.platformio.org/en/latest/librarymanager/config.html#flags using build.flags

   {
   .... 
   "repository": {
       "type": "hg",
       "url": "https://os.mbed.com/teams/Semtech/code/SX1276Lib/"
   },
   "build": {
       "flags": "-Iradio -Ienums -Iregisters -Iregisters -Isx1276 -Itypedefs"
   }
   }

   Flags could be a string or list. We can organize includes using array.

2. Import extraIncludes from module.json if exists into build.flags. See above.

[ivankravets]

/cc @MrSurly