Feature: Add basic support for DJI drone import

[fxstein]

Enable the import from DJI drone sd-cards similar to the GoPro media.

Since there is no version text file on the sd-cards of DJI drones, it requires some directory/filename logic to identify as a DJI drone.

Won't be able to recognize the drone type or serial number, but at least the fact that it is DJI drone media.

➜  tree -d
.
├── DCIM
│   └── 100MEDIA
├── LOST.DIR
└── MISC
    ├── GIS
    ├── IDX
    └── THM
        └── 100

9 directories

➜  MISC tree   
.
├── GIS
│   └── dji.gis
├── IDX
├── IDX_BLOCK
└── THM
    └── 100
        ├── DJI_0001.SCR
        ├── DJI_0001.THM
        ├── DJI_0002.SCR
        ├── ...
        ├── DJI_0524.THM
        ├── DJI_0525.SCR
        └── DJI_0525.THM