add perference header for legacy preference
use custmoized PreferenceFragment for pre 3.0 compatible

fix haiwen/seadroid#124
optimize Gesture Lock
add backward compatibility support

1. create a new package "com.seafile.seadroid2.gesturelock"
2. add Chinese translations
code cleanup
remove hard code strings

translate Chinese strings
add Gesture Lock layout screen size adaptation
code cleanup

close #124
add backward compatibility support

1. create a new package "com.seafile.seadroid2.gesturelock"
2. add Chinese translations
code cleanup
Merge branch 'pullToRefresh' of github.com:Logan676/seadroid into pullToRefresh
add pull to refresh to ActivitiesFragment