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
code add paddings to Gesture Lock layout
change text color for button
fix get photo path from external SD card #140
update README and pom files
code cleanup
code cleanup
update Utils
fix #150
Merge pull request #152 from Logan676/bug

fix Images being uploaded over 4G even with "Wifi only" selected #150
Merge pull request #149 from Logan676/uphome

fix actionbar home up button in AccountDetailActivity does not work as expected #139
Merge pull request #148 from Logan676/camera

fix get photo path from external SD card #140
Revert "Merge pull request #148 from Logan676/camera"

This reverts commit 6e3fb44e56d331ba3aca0166afbaa598e5d585d5, reversing
changes made to 43535712ba5c47649a0a14ac8cb49d2ff8e38f95.