Delete extra Gecko files before shallow flash.
Base on the `flash_gecko()` function of `flash.sh` from B2G project [1].

1. remove /system/media on device (it seems like we don't need this folder...)
2. remove the extra Gecko files on device
3. shallow flash Gecko files into device

[1]: https://github.com/mozilla-b2g/B2G/blob/master/flash.sh#L262-L267
console download progress
Merge pull request #290 from SteveALee/shallowflashbat

Fixed stupid minor bug
Merge pull request #291 from zapion/download_progress

console download progress
Added console download progress for window mode.
Merge pull request #292 from askeing/add_progress_for_window_mode

Added console download progress for window mode.
Added flash_local.py for GUI user...
Merge pull request #283 from askeing/clean_extra_gecko_files_before_flash

Delete extra Gecko files before shallow flash.
Merge pull request #293 from askeing/flash_local_GUI

Added flash_local.py for GUI user...
Support more than one devices for flash_local.py
Merge pull request #294 from askeing/support_more_devices_for_flash_local

Support more than one devices for flash_local.py
Changed the flash seq from "gaia->gecko" to "gecko->gaia".
Added /system/b2g/defaults/ and /system/b2g/webapps/ to white list of clean_extra_gecko_files().
fixed #295
Merge pull request #296 from askeing/fix_295

Changed the flash seq from "gaia->gecko" to "gecko->gaia". Added "webapps" and "defaults" into white list of clean gecko method.
Run Cygwin setup to simplify it