Layed foundations for the shell commands cards + added CardButton, a card with a button which executes the shell command passed in the <command> tag.

Pro tip: pass the location of a script in the <command tag> in order to execute several commands at once.
Example:
<tweak type=shell><control type=button text=APPLY/><command>sh /sdcard/.APKreator/myscript.sh</command><name>Test</name><description>lorem ipsum dolor sit amet</description>