Add Retrobat support

[detain]

Differences ive noticed so far from normal emulationstation which need to be incorporated into the retrobat frontend code:

• <game> tags have an id="xxxxx" attribute
• adds fanart image type
• adds region field
• adds md5 field
• adds gametime field
• adds family field
• adds emulator field
• doesn't use the texture field from skyscraper
• doesn't use the rating field from skyscraper
• doesn't use the kidgame field from skyscraper
• images and videos are stored in roms//images/ and roms//videos/ folders matching the rom filename plus a suffix, -thumb, -marquee, -image, -fanart