switched to right handedness and added tax and tip buttons
static tax and tip applied
made prefs for tax and tip.
todo:
on change listener for tax and tip
limit text input value to numerical
update pref from screen
limit numeric preferences
made "no" button abstracted preferences control
took out subtract button
set tip. not tested change
tested change tip. good
resolved #7 and resolved #8
Merge pull request #23 from codebunny/alice

tax & tip