stack view shows 6 lines and has no word wrap
clip stack and memory view items horizontally
add integer layout
add undo stack class (forgotten files)
toggle buttons radio groups implemented

Usage:
    <me.kstep.ucalc.widgets.UToggleButton ucalc:radio_group="group" android:text="one" />
    <me.kstep.ucalc.widgets.UToggleButton ucalc:radio_group="group" android:text="two" />

Clicking on any of button to switch it on switches off all buttons with
the same radio_group value. Radio groups are stored in
HashMap<String,ArrayList<UToggleButton>> and thus are quite effective.
units category UI implemented (WIP)
fixed null pointer exception bug in units simplification
units division and multiplication by Unit.NONE is original unit itself
shortcut operations with NONE unit
use more robust .equals() compare for units arithmetics
turn off redundant null sanity check during multiple unit simplification
update gitignore file
fix simplification bug: equal units doesn't equals in HashMap
hashing offsets increased
distinct none unit name ("1")
tests update
autogenerated name tracking during MultipleUnit simplification
numbers equality fix
units test cleaned up
remove debug prints