Add a setting to display battery information

[isalgueiro]

Thanks for sharing this launcher, it's my preferred choice for Android TV boxes.

This year O Apalpador was kind enough to get me a Retroid Pocket 2; the thing is something like a portable console, without a touchscreen, and running Android, so I installed this launcher on it to make it easier to use with the d-pad.

It's working like a charm, but I'm missing some battery information in the home screen, so I made this little patch:

• This is disabled by default, so this doesn't show 0% ? on devices without a battery
• I use whatever BatteryManager thinks is the right icon for the current battery status. I find that icon pretty ugly in every device I tested this on, so in the future I may add a custom drawable to use as battery status icon.
• No idea if the translations are right, I just used google translate here.
• Tested on said Retroid thing and in an Android TV emulator at 720p.

Hope you find this patch useful. Happy holidays!

[coveralls]

Coverage remained the same at 0.0% when pulling b50a0cb on isalgueiro:battery-info into 8cf33ab on alescdb:master.

[alescdb]

LGTM.
Thanks for the PR ! :-)