obvious fix for header click handler

if user do not provide "OnHeaderClickListener", the header view will not be clickable,
so user will be able to "get" to the underlying views and handle clicks by himself
add ExpandableStickyListHeaderListView which enable listview to expand/collapse sub items
addFooterView(View v, Object data, boolean isSelectable) is missing
Merge pull request #1 from emilsjolander/master

sync with master
add ExpandableListTestActivity
Merge remote-tracking branch 'origin/master'
simplify IAnimationExecutor
update ExpandableListTextActivity
fix divider height calculate logic when collapse items
Update build tools
Merge pull request #307 from Eng-Fouad/patch-1

addFooterView(View v, Object data, boolean isSelectable) is missing
Support negative top offset. Fixes #308
Fix crash in sample
Make sure sticky header martches parent in width
changes some variable names to improve readability
update  class access-modifier
update  class access-modifier
fix current header touch interception,
update current header click listener when setOnHeaderClickListener called
update readme
small code refactoring