Update Makefile after GNU conventions

For more information, see https://www.gnu.org/prep/standards/html_node/Makefile-Conventions.html#Makefile-Conventions

Added GPL3 license notice to files

• Added GPL3 license notice in bash script
• Added GPL3 license notice in Makefile

Fix filemode from executable

• Let a normal user execute the script.

Fix Makefile to meet OBS requirements

• Do not set owner in Makefile

First version to be build and distributed through OBS

Features

• how much battery power is left
• how much time it is left
• how much time is needed for recharging